Effects of Elevated CO2 on Plant Chemistry, Growth, Yield of Resistant Soybean, and Feeding of a Target Lepidoptera Pest, Spodoptera litura (Lepidoptera: Noctuidae)

Effects of Elevated CO2 on Plant Chemistry, Growth, Yield of Resistant Soybean, and Feeding of a... Abstract Atmospheric CO2 level arising is an indisputable fact in the future climate change, as predicted, it could influence crops and their herbivorous insect pests. The growth and development, reproduction, and consumption of Spodoptera litura (F.) (Lepidoptera: Noctuidae) fed on resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean grown under elevated (732.1 ± 9.99 μl/liter) and ambient (373.6 ± 9.21 μl/liter) CO2 were examined in open-top chambers from 2013 to 2015. Elevated CO2 promoted the above- and belowground-biomass accumulation and increased the root/shoot ratio of two soybean cultivars, and increased the seeds’ yield for Lamar. Moreover, elevated CO2 significantly reduced the larval and pupal weight, prolonged the larval and pupal life span, and increased the feeding amount and excretion amount of two soybean cultivars. Significantly lower foliar nitrogen content and higher foliar sugar content and C/N ratio were observed in the sampled foliage of resistant and susceptible soybean cultivars grown under elevated CO2, which brought negative effects on the growth of S. litura, with the increment of foliar sugar content and C/N ratio were greater in the resistant soybean in contrast to the susceptible soybean. Furthermore, the increment of larval consumption was less than 50%, and the larval life span was prolonged more obvious of the larvae fed on resistant soybean compared with susceptible soybean under elevated CO2. It speculated that the future climatic change of atmospheric CO2 level arising would likely cause the increase of the soybean yield and the intake of S. litura, but the resistant soybean would improve the resistance of the target Lepidoptera pest, S. litura. elevated carbon dioxide, resistant soybean, plant chemistry, growth and yield, development and consumption Human influence on the climate system is clear and recent anthropogenic emissions of greenhouse gases are the highest in history (IPCC 2014). Atmospheric carbon dioxide (CO2) concentration has increased by more than 44%, from 280 ppm in the pre-industrial period (IPCC 2014) to 404 ppm in October of 2017 (www.esrl.noaa.gov/gmd/ccgg/trends/) and it is projected to increase to 550 ppm by 2050 and may surpass to 700 ppm by 2100 (Stocker et al. 2013). The atmospheric CO2 level arising has received considerable attention because it has marked effects on plant phytochemistry, growth and yield, and feeding behavior of phytophagous insect pests, which can in turn influence agro-ecosystem processes and crop productivity (Norby et al. 2005, Zvereva and Kozlov 2006, Lindroth 2010, O’Neill et al. 2010, Ainsworth et al. 2012a). The atmospheric CO2 concentration arising is likely to affect biota indirectly via climate change, and directly by producing changes not only in plant growth and allocation, but also in plant tissue chemical composition (Srinivasa et al. 2012). Legumes, more responsive to elevated CO2 than other plants, will have a competitive advantage when growing under elevated CO2 (Ainsworth and Long 2005). Elevated CO2 is generally expected to enhance the photosynthesis of crop species which utilize the C3 photosynthetic pathway (Drake et al. 1997, Ziska et al. 1997, Kim et al. 2003), leading to increases in the growth, yields and C/N ratios of agricultural crops (Bazzaz 1990, Horie et al. 2000, Kimball et al. 2002). The interactions between insect pests and their host plants change in response to the effects of CO2 on plant nutritional quality (Chen et al. 2005, Ainsworth et al. 2007). Due to the accumulation of nonstructural carbohydrates of plants grown under elevated CO2 (Williams et al. 1998), it declined the nutritional quality of plant leaves (Coley 1998). Many insects, especially some Lepidoptera insects will confront less nutritious host plants under elevated CO2, which will prolong the larval developmental duration and increase their intake (e.g. Helicoverpa armigera, Chen et al. 2005, Orgyia leucostigma, Lindroth et al. 2002). Soybean (Glycine max [L.] Merr.) is one of the important crops with high contents of edible protein and oil (Ainsworth et al. 2012b). Elevated CO2 caused a significant increase in total biomass and seed yield of the high photosynthetic efficiency soybean cultivars (Su et al. 2016). Spodoptera litura (F.) (Lepidoptera: Noctuidae) is a major leaf-chewing herbivorous insect of soybean, and it can cause heavily yield losses (Armes et al. 1997). In fact, the applying resistant soybean accessions would contribute to the integrated pest management in a sustainable and environment-friendly manner (Chen et al. 2012). Among the plant introductions from USDA Soybean Germplasm Collection, PI229358 was used in resistant breeding against insect pests because of multiple resistances to several species of herbivorous insects, especially some leaf-chewing insects (Lambert and Kilen 1984, Rowan et al. 1991). The soybean cultivar Lamar (PI533604) was selected and bred through cross-breeding with its resistant parental line PI229358 in Mississippi Agriculture and Forestry Experiment station (Hartwig et al. 1990). Lamar is considered as a highly resistant cultivar of soybean against S. litura and JLNMH as highly susceptible soybean cultivar for S. litura (Wu et al. 2006, Xing et al. 2017). Even though some studies have reported the effects of elevated CO2 on soybean and the herbivorous insect (Aldea et al. 2005, Hamilton et al. 2005, Zavala et al. 2009, Casteel et al. 2012, Murray et al. 2013). However, studies about the use of plants that differ in their resistance to a chewing herbivore are novel. We hypothesized that 1) the interaction between the chemical components in plants and the growth, development, and fecundity of chewing herbivores might be various in different resistant cultivars of soybean under elevated CO2, and 2) elevated CO2 might be more beneficial to the growth, yield, and resistance performance against insects in resistant soybeans than that of to susceptible soybeans. In this study, we used two soybean cultivars (i.e., the resistant cv. Lamar and the susceptible cv. JLNMH) to evaluate the impacts of elevated CO2 and resistant soybean on plant chemistry, growth, and yield of soybean and the relationship between plant chemistry change of resistant soybean and the growth, development, reproduction, and consumption of S. litura under elevated CO2. Materials and Methods Open-Top Chambers Six open-top chambers (OTCs, Granted Patent: ZL201120042889.1; 2.5 m in height × 3.2 m in diameter) (Chen et al. 2011) were constructed at the Innovation Research Platforms for Climate Change, Biodiversity and Pest Management (CCBPM; http://www.ccbpm.org) in Ningjin County, Shandong Province of China (37°38′ 30.7′′ N, 116°51′ 11.0′′ E). Two levels of atmospheric CO2 concentration were applied continuously, i.e., ambient level (2013: 368.5 ± 18.3 μl/liter, 2014: 384.2 ± 14.8 μl/liter, 2015: 368.0 ± 14.8 μl/liter; mean: 373.6 ± 9.21 μl/liter) and elevated level (2013: 723.6 ± 20.3 μl/liter, 2014: 743.1 ± 19.2 μl/liter, 2015: 729.6 ± 23.5 μl/liter; mean: 732.1 ± 9.99 μl/liter), representing the predicted level in about 100 yr (Watson et al. 1996, Houghton et al. 2001), from 14 June to 13 October in 2013, 2014, and 2015, respectively. Three OTCs were used for each CO2 treatment, and the CO2 concentration in each OTC was monitored continuously and adjusted with an infrared CO2 analyzer (Ventostat 8102; Telaire Company, Goleta, CA) on every day to ensure relatively stable CO2 concentrations. The OTCs with elevated CO2 were injected with canned CO2 gas with 95% purity and controlled via automated CO2 concentration monitor (Chen and Ge 2004). Air temperature and relative humidity were monitored continuously by using an automatic temperature analysis system (U23-001, HOBO Pro V2 Temp/RH Data Logger; MicroDAQ.com, Ltd, Contoocook, NH, USA) in each OTC throughout the field experiment. Actual mean temperature and relative humidity from 2013 to 2015 were shown in Table 1. Table 1. Actual mean temperature and relative humidity in the OTCs of ambient CO2 (i.e., aCO2) and elevated CO2 (i.e., eCO2) from 14 June to 13 October in 2013, 2014, and 2015, respectively (Mean ± SD) Year  CO2 treatments  Actual temperature (°C, 24 h/d)  Actual relative humidity (%, 24 h/d)  2013  eCO2  26.93 ± 0.36a  45.12 ± 2.97a  aCO2  26.41 ± 0.12a  46.34 ± 2.80a  2014  eCO2  27.12 ± 0.49a  48.75 ± 4.65a  aCO2  26.74 ± 0.21a  49.53 ± 4.14a  2015  eCO2  26.64 ± 0.36a  47.76 ± 2.31a  aCO2  26.30 ± 0.29a  51.48 ± 3.26a  Year  CO2 treatments  Actual temperature (°C, 24 h/d)  Actual relative humidity (%, 24 h/d)  2013  eCO2  26.93 ± 0.36a  45.12 ± 2.97a  aCO2  26.41 ± 0.12a  46.34 ± 2.80a  2014  eCO2  27.12 ± 0.49a  48.75 ± 4.65a  aCO2  26.74 ± 0.21a  49.53 ± 4.14a  2015  eCO2  26.64 ± 0.36a  47.76 ± 2.31a  aCO2  26.30 ± 0.29a  51.48 ± 3.26a  The same lowercase letters indicate no significant difference between ambient and elevated CO2 in same year by the Duncan’s test at P > 0.05. View Large Table 1. Actual mean temperature and relative humidity in the OTCs of ambient CO2 (i.e., aCO2) and elevated CO2 (i.e., eCO2) from 14 June to 13 October in 2013, 2014, and 2015, respectively (Mean ± SD) Year  CO2 treatments  Actual temperature (°C, 24 h/d)  Actual relative humidity (%, 24 h/d)  2013  eCO2  26.93 ± 0.36a  45.12 ± 2.97a  aCO2  26.41 ± 0.12a  46.34 ± 2.80a  2014  eCO2  27.12 ± 0.49a  48.75 ± 4.65a  aCO2  26.74 ± 0.21a  49.53 ± 4.14a  2015  eCO2  26.64 ± 0.36a  47.76 ± 2.31a  aCO2  26.30 ± 0.29a  51.48 ± 3.26a  Year  CO2 treatments  Actual temperature (°C, 24 h/d)  Actual relative humidity (%, 24 h/d)  2013  eCO2  26.93 ± 0.36a  45.12 ± 2.97a  aCO2  26.41 ± 0.12a  46.34 ± 2.80a  2014  eCO2  27.12 ± 0.49a  48.75 ± 4.65a  aCO2  26.74 ± 0.21a  49.53 ± 4.14a  2015  eCO2  26.64 ± 0.36a  47.76 ± 2.31a  aCO2  26.30 ± 0.29a  51.48 ± 3.26a  The same lowercase letters indicate no significant difference between ambient and elevated CO2 in same year by the Duncan’s test at P > 0.05. View Large Soybean Cultivars and Treatment Setup The resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean cultivars to S. litura were selected in this study. These two soybean cultivars were both supplied by the National Center for Soybean Improvement, Nanjing Agricultural University. Four treatments of both CO2 levels and two soybean cultivars were set up, including: 1) resistant soybean grown in ambient CO2 (aLamar), 2) resistant soybean grown in elevated CO2 (eLamar), 3) susceptible soybean grown in ambient CO2 (aJLNMH), and 4) susceptible soybean grown in elevated CO2 (aJLNMH). From 2013 to 2015, the resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean cultivars were planted in plastic buckets (diameter × height = 30 cm × 45 cm) filled with 2: 1 (by volume) loam: organic cultivation substrate and randomly placed in chambers on 14 June in 2013, 2014, and 2015, respectively. Nine buckets for each soybean cultivar were placed randomly in each OTC, and 10 soybean seeds were sown in each bucket. When plants reached the V4 (fourth compound leaves) stage (Fehr et al. 1971), extra plants were thinned out and six plants remained in each bucket. No chemical fertilizers or insecticides were used during the experiment. To standardize soil moisture across treatments, each bucket was irrigated with 2 liters water once every 4 d during the whole experimental period. Soybean Growth Traits, Yield, and Foliar Sugar and N Contents During the R4 (full pods) stage of soybean plants (Fehr et al. 1971), one bucket was randomly selected from each treatment of aLamar, eLamar, aJLNMH, and eJLNMH, respectively. Three sampled plants were dried at 80°C for 72 h and measured the dry weight per plant (including aboveground and belowground weight), and nine leaves from other three sampled plants (three leaflets from each sampled plant at same leaf position) were fixated at 105°C for 30 min, then oven-dried at 80°C for 72 h and weighted the dry weight per leaf. Moreover, the sampled dry leaves were grounded into powder, and then analyzed the contents of foliar sugar (anthrone colorimetry) (Zhu and Hong 2008), nitrogen (Kjeldahl method) (EMBRAPA 2009) and the C/N ratio (sugar content/nitrogen content) (Deng et al. 2012). During the R6 (full seeds) stage of soybean plants (Fehr et al. 1971), in the same way, dry weight per plant, contents of foliar sugar, N, and C/N ratio, were calculated. At the R8 stage (i.e., full maturity; Fehr et al. 1971), the soybean plants of the four treatments of aLamar, eLamar, aJLNMH, and eJLNMH were harvested and nine soybean plants were randomly selected from each OTC to measure the seed weight per plant, respectively. Insect Stocks and Rearing Egg masses of S. litura were collected from the Henan Jiyuan Baiyun Industrial Co., Ltd, and reared in the growth chambers (Model: GXZ-500B; Accuracy: temp: ±1°C, humidity: ±1%; Manufacturer: Ningbo JIANGNAN Ltd., Ningbo, China) under the control environment (temp: 27 ± 1°C; photoperiod: 14:10 (L:D) h; relative humidity: 70 ± 10%) for incubation. Twenty neonate larvae as one replication were placed in a disinfected plastic box (150 mm in diameter and 100 mm in height). Three replications (60 larvae) were kept for each treatment of two CO2 levels and two soybean cultivars, i.e., total 240 larvae for the whole experiment. The bioassay was done at growth chamber and the larvae of S. litura were fed with different sources of soybean from OTCs. Neonate larvae were reared on detached leaves of two soybean cultivars grown in two CO2 levels in the respective OTCs. The feeding trial was conducted between the R4 (full pods) and R6 (full seeds) stages of soybean plants (Fehr et al. 1971). The detached leaves were collected daily and randomly taken from the two soybean cultivars grown in two CO2 levels (the same leaf position at each collection) and used for the rearing after cleaning and drying. Two leaves were extracted, one of them was weighed and dried at 80°C for 72 h and measured the dry weight using electronic balance (Model: AL104; Accuracy: ±0.1 mg; METTLER-TOLEDO, Switzerland) in order to compute the foliar ratio of dry weight divided by fresh weight (i.e., DW/FW). The other one was offered to the larvae after weighing, and 24 h later the rest of this leaf and fecal matter of S. litura were dried at 80°C for 72 h to measure their dry weight by using the foliar ratio of DW/FW. Moreover, the consumption of larvae was calculated by using the mean leaf weight consumed minus the fecal matter weight per larva. The same process was repeated each day until the larvae grown to the third instar, and then the large larvae were fed separately in marked glass Petri dish (diameter:height = 60:16 mm), considering the cannibalism of old/late instar larvae of S. litura (Deng et al. 2015). In the same way of feeding mentioned above, the leaf weight consumed and the fecal matter weight per larva were calculated based on the above same protocol. In this process, once the larvae die, the corresponding record was deleted. When the larvae halted eating, a part of larvae were dried at 80°C for 72 h and measured the dry weight, and another part of larvae were collected until pupation. Growth, Development, and Fecundity of S. litura During the entire experiment, the tested larvae of S. litura were reared with new detached soybean leaves from the four treatments of aLamar, eLamar, aJLNMH, and eJLNMH, and simultaneously removed the excrements of S. litura larvae every day; the ecdysis and development of larvae were observed and recorded three times every day (average interval 8 h). The total consumption and fecal matter per larva were calculated. The pupal weight of S. litura was recorded on the second day after pupation, and the adult eclosion was also observed. After eclosion, S. litura moths were allowed for mating in cages (35 cm in length × 35 cm in width × 40 cm in height), and the paired moths of one female and one male were put in a plastic cup (8 cm in diameter × 20 cm in height) with a net cover of degreased cotton yarn for oviposition, and these adults were fed with 10% honey solution. The cotton yarns were replaced every day and the eggs laid on each disc were counted and recorded daily. Data Analysis All data were analyzed by using the SAS v. 9.4. The Levene’s test was used to test the homoscedasticity of variances (P > 0.10), and the Shapiro-Wilk test was used to examine the normality of the experimental data (P > 0.05). Moreover, three-factor ANOVAs were used to identify the influence of CO2 levels (elevated CO2 vs. ambient CO2), soybean cultivars (the resistant cv. Lamar vs. the susceptible cv. JLNMH), sampling years (2013, 2014, 2015), and their bi- and tri-interactions on the biomass, yield and foliar chemistry of soybean, and on the growth, development and reproduction, feeding and excretion of S. litura. The measured indexes of soybean include the aboveground and belowground biomass, root/shoot ratio, foliar sugar and N contents, foliar C/N ratio, and seeds weight of soybean plants. The measured indexes of S. litura include feeding and excretion amount and net consumption per larva, larval and pupal life span, larval and pupal weight, and fecundity. Moreover, the Duncan’s test was used to analyze the significant difference in the measured indexes of soybean and S. litura between ambient and elevated CO2 for same soybean cultivar, and between the resistant and susceptible soybean cultivars under same CO2 level at P < 0.05, respectively. Furthermore, the Pearson’s correlation analysis was used to analyze the significant difference between the measured indexes of the foliar chemistry of soybean and the growth of S. litura in different of CO2 levels (elevated vs. ambient) and sampling years (2013, 2014 and 2015) at P < 0.05, 0.01 or 0.001. Results Effects of Soybean Cultivar and Elevated CO2 on the Growth, Foliar Chemistry, and Yield of Soybean CO2 levels and soybean cultivars significantly affected the aboveground biomass, foliar sugar and N contents, foliar C/N ratio both at R4 and R6 stages of soybean, and the seeds weight per plant (P < 0.01 or 0.001; Table 2); the belowground biomass was significantly affected by soybean cultivars both at R4 and R6 stages (P < 0.05 and 0.001; Table 2), and significantly affected by CO2 levels at R6 stage (P < 0.05; Table 2); the root/shoot ratio was just significantly affected by soybean cultivars at R4 stage (P < 0.05; Table 2). Moreover, there was a significant difference in the seeds weight per plant among sampling years (P < 0.001; Table 2). Table 2. Three-way ANOVA of CO2 levels (elevated vs. ambient), soybean cultivars (resistant vs. susceptible), sampling years (2013, 2014 and 2015) and their bi- and tri-interactions on the biomass, foliar chemistry at the R4 (full pods) and the R6 (full seeds) stages, and the yield at the R8 (full maturity) stage of soybean plants, and on the growth, development and reproduction, feeding and excretion of Spodoptera litura in 2013–2015 (F values) Measured indexes  CO2a  Cv.b  Year  CO2 × Cv.  CO2 × year  Year × Cv.  Year × CO2 × Cv.  Soybean  R4  Aboveground biomass (dry weight; g/plant)  9.1†  36.7‡  0.4  0.2  0.1  0.3  0.9  Belowground biomass (dry weight; g/plant)  1.1  5.3*  1.5  0.1  0.2  0.3  0.0  Root/shoot ratio (%)  1.6  5.0*  1.0  1.2  0.2  0.9  0.1  Foliar sugar (%)  109.0‡  110.3‡  0.1  21.7‡  0.1  1.1  0.1  Foliar nitrogen (%)  20.3‡  123.8‡  0.3  0. 9  0.8  0.3  0.1  Foliar C/N ratio  54.9‡  127.5‡  0.1  17.3‡  0.4  0.1  0.2  R6  Aboveground biomass (dry weight; g/plant)  23.4‡  95.3‡  0.8  0.6  1.1  0.2  0.4  Belowground biomass (dry weight; g/plant)  5.7*  28.9‡  0.4  1.3  0.4  0.4  0.0  Root/shoot ratio (%)  0.8  1.4  0.1  0.2  0.1  0.1  0.0  Foliar sugar (%)  50.1‡  81.4‡  0.3  10.7†  0.1  0.1  0.2  Foliar nitrogen (%)  36.9‡  400.5‡  3.4  0.0  3.1  1.2  0.5  Foliar C/N ratio  132.7‡  547.0‡  0.3  42.6‡  3.0  0.1  0.9  R8  Seeds weight (dry weight; g/plant)  45.1‡  1399.3‡  10.0‡  17.5‡  1.7  4.9*  0.2  S. litura  Larval life span (day)  50.8‡  114.4‡  2.6  10.0†  0.8  0.8  0.3  Pupal life span (day)  16.5‡  126.4‡  0.3  0.9  0.6  0.5  0.5  Larval weight (g)  172. 0‡  779.3‡  0.4  28.2‡  5.0*  0.4  0.3  Pupal weight (g)  20.4‡  178.7‡  1.7  1.5  0.3  1.1  0.8  Fecundity (eggs laid per female)  49.6‡  790.7‡  0.3  0.0  0.1  3.8*  0.8  Feeding amount (dry weight; g/larva)  753.8‡  3850.5‡  2.0  323.5‡  1.5  0.4  1.2  Excretion amount (dry weight; g/larva)  577.1‡  3448.0‡  1.3  67.0‡  0.2  0.3  0.4  Net consumption (dry weight; g/larva)  840.0‡  3825.5‡  4.9*  636.2‡  5.9†  2.5  5.3†  Measured indexes  CO2a  Cv.b  Year  CO2 × Cv.  CO2 × year  Year × Cv.  Year × CO2 × Cv.  Soybean  R4  Aboveground biomass (dry weight; g/plant)  9.1†  36.7‡  0.4  0.2  0.1  0.3  0.9  Belowground biomass (dry weight; g/plant)  1.1  5.3*  1.5  0.1  0.2  0.3  0.0  Root/shoot ratio (%)  1.6  5.0*  1.0  1.2  0.2  0.9  0.1  Foliar sugar (%)  109.0‡  110.3‡  0.1  21.7‡  0.1  1.1  0.1  Foliar nitrogen (%)  20.3‡  123.8‡  0.3  0. 9  0.8  0.3  0.1  Foliar C/N ratio  54.9‡  127.5‡  0.1  17.3‡  0.4  0.1  0.2  R6  Aboveground biomass (dry weight; g/plant)  23.4‡  95.3‡  0.8  0.6  1.1  0.2  0.4  Belowground biomass (dry weight; g/plant)  5.7*  28.9‡  0.4  1.3  0.4  0.4  0.0  Root/shoot ratio (%)  0.8  1.4  0.1  0.2  0.1  0.1  0.0  Foliar sugar (%)  50.1‡  81.4‡  0.3  10.7†  0.1  0.1  0.2  Foliar nitrogen (%)  36.9‡  400.5‡  3.4  0.0  3.1  1.2  0.5  Foliar C/N ratio  132.7‡  547.0‡  0.3  42.6‡  3.0  0.1  0.9  R8  Seeds weight (dry weight; g/plant)  45.1‡  1399.3‡  10.0‡  17.5‡  1.7  4.9*  0.2  S. litura  Larval life span (day)  50.8‡  114.4‡  2.6  10.0†  0.8  0.8  0.3  Pupal life span (day)  16.5‡  126.4‡  0.3  0.9  0.6  0.5  0.5  Larval weight (g)  172. 0‡  779.3‡  0.4  28.2‡  5.0*  0.4  0.3  Pupal weight (g)  20.4‡  178.7‡  1.7  1.5  0.3  1.1  0.8  Fecundity (eggs laid per female)  49.6‡  790.7‡  0.3  0.0  0.1  3.8*  0.8  Feeding amount (dry weight; g/larva)  753.8‡  3850.5‡  2.0  323.5‡  1.5  0.4  1.2  Excretion amount (dry weight; g/larva)  577.1‡  3448.0‡  1.3  67.0‡  0.2  0.3  0.4  Net consumption (dry weight; g/larva)  840.0‡  3825.5‡  4.9*  636.2‡  5.9†  2.5  5.3†  aCO2: CO2 levels (elevated vs. ambient). bCv.: Soybean cultivars (resistant vs. susceptible). *P < 0.05, †P < 0.01, ‡P < 0.001. View Large Table 2. Three-way ANOVA of CO2 levels (elevated vs. ambient), soybean cultivars (resistant vs. susceptible), sampling years (2013, 2014 and 2015) and their bi- and tri-interactions on the biomass, foliar chemistry at the R4 (full pods) and the R6 (full seeds) stages, and the yield at the R8 (full maturity) stage of soybean plants, and on the growth, development and reproduction, feeding and excretion of Spodoptera litura in 2013–2015 (F values) Measured indexes  CO2a  Cv.b  Year  CO2 × Cv.  CO2 × year  Year × Cv.  Year × CO2 × Cv.  Soybean  R4  Aboveground biomass (dry weight; g/plant)  9.1†  36.7‡  0.4  0.2  0.1  0.3  0.9  Belowground biomass (dry weight; g/plant)  1.1  5.3*  1.5  0.1  0.2  0.3  0.0  Root/shoot ratio (%)  1.6  5.0*  1.0  1.2  0.2  0.9  0.1  Foliar sugar (%)  109.0‡  110.3‡  0.1  21.7‡  0.1  1.1  0.1  Foliar nitrogen (%)  20.3‡  123.8‡  0.3  0. 9  0.8  0.3  0.1  Foliar C/N ratio  54.9‡  127.5‡  0.1  17.3‡  0.4  0.1  0.2  R6  Aboveground biomass (dry weight; g/plant)  23.4‡  95.3‡  0.8  0.6  1.1  0.2  0.4  Belowground biomass (dry weight; g/plant)  5.7*  28.9‡  0.4  1.3  0.4  0.4  0.0  Root/shoot ratio (%)  0.8  1.4  0.1  0.2  0.1  0.1  0.0  Foliar sugar (%)  50.1‡  81.4‡  0.3  10.7†  0.1  0.1  0.2  Foliar nitrogen (%)  36.9‡  400.5‡  3.4  0.0  3.1  1.2  0.5  Foliar C/N ratio  132.7‡  547.0‡  0.3  42.6‡  3.0  0.1  0.9  R8  Seeds weight (dry weight; g/plant)  45.1‡  1399.3‡  10.0‡  17.5‡  1.7  4.9*  0.2  S. litura  Larval life span (day)  50.8‡  114.4‡  2.6  10.0†  0.8  0.8  0.3  Pupal life span (day)  16.5‡  126.4‡  0.3  0.9  0.6  0.5  0.5  Larval weight (g)  172. 0‡  779.3‡  0.4  28.2‡  5.0*  0.4  0.3  Pupal weight (g)  20.4‡  178.7‡  1.7  1.5  0.3  1.1  0.8  Fecundity (eggs laid per female)  49.6‡  790.7‡  0.3  0.0  0.1  3.8*  0.8  Feeding amount (dry weight; g/larva)  753.8‡  3850.5‡  2.0  323.5‡  1.5  0.4  1.2  Excretion amount (dry weight; g/larva)  577.1‡  3448.0‡  1.3  67.0‡  0.2  0.3  0.4  Net consumption (dry weight; g/larva)  840.0‡  3825.5‡  4.9*  636.2‡  5.9†  2.5  5.3†  Measured indexes  CO2a  Cv.b  Year  CO2 × Cv.  CO2 × year  Year × Cv.  Year × CO2 × Cv.  Soybean  R4  Aboveground biomass (dry weight; g/plant)  9.1†  36.7‡  0.4  0.2  0.1  0.3  0.9  Belowground biomass (dry weight; g/plant)  1.1  5.3*  1.5  0.1  0.2  0.3  0.0  Root/shoot ratio (%)  1.6  5.0*  1.0  1.2  0.2  0.9  0.1  Foliar sugar (%)  109.0‡  110.3‡  0.1  21.7‡  0.1  1.1  0.1  Foliar nitrogen (%)  20.3‡  123.8‡  0.3  0. 9  0.8  0.3  0.1  Foliar C/N ratio  54.9‡  127.5‡  0.1  17.3‡  0.4  0.1  0.2  R6  Aboveground biomass (dry weight; g/plant)  23.4‡  95.3‡  0.8  0.6  1.1  0.2  0.4  Belowground biomass (dry weight; g/plant)  5.7*  28.9‡  0.4  1.3  0.4  0.4  0.0  Root/shoot ratio (%)  0.8  1.4  0.1  0.2  0.1  0.1  0.0  Foliar sugar (%)  50.1‡  81.4‡  0.3  10.7†  0.1  0.1  0.2  Foliar nitrogen (%)  36.9‡  400.5‡  3.4  0.0  3.1  1.2  0.5  Foliar C/N ratio  132.7‡  547.0‡  0.3  42.6‡  3.0  0.1  0.9  R8  Seeds weight (dry weight; g/plant)  45.1‡  1399.3‡  10.0‡  17.5‡  1.7  4.9*  0.2  S. litura  Larval life span (day)  50.8‡  114.4‡  2.6  10.0†  0.8  0.8  0.3  Pupal life span (day)  16.5‡  126.4‡  0.3  0.9  0.6  0.5  0.5  Larval weight (g)  172. 0‡  779.3‡  0.4  28.2‡  5.0*  0.4  0.3  Pupal weight (g)  20.4‡  178.7‡  1.7  1.5  0.3  1.1  0.8  Fecundity (eggs laid per female)  49.6‡  790.7‡  0.3  0.0  0.1  3.8*  0.8  Feeding amount (dry weight; g/larva)  753.8‡  3850.5‡  2.0  323.5‡  1.5  0.4  1.2  Excretion amount (dry weight; g/larva)  577.1‡  3448.0‡  1.3  67.0‡  0.2  0.3  0.4  Net consumption (dry weight; g/larva)  840.0‡  3825.5‡  4.9*  636.2‡  5.9†  2.5  5.3†  aCO2: CO2 levels (elevated vs. ambient). bCv.: Soybean cultivars (resistant vs. susceptible). *P < 0.05, †P < 0.01, ‡P < 0.001. View Large Compared with ambient CO2, elevated CO2 significantly increased the aboveground biomass, foliar sugar content and C/N ratio of the resistant and susceptible soybean at the R4 (Lamar: +20.28, +27.08, and +51.09%; JLNMH: +10.88, +11.72, and +22.58%) and R6 (Lamar: +17.47, +21.43, and +44.44%; JLNMH: +17.54, +9.30, and +21.92%) stages respectively (P < 0.05; Table 3), and significantly increased the belowground biomass of the susceptible soybean at the R6 stage (+13.96%; P < 0.05; Table 3). Moreover, elevated CO2 reduced the root/shoot ratio at the R4 and R6 stages of resistant and susceptible soybean respectively, but not significantly compared with ambient CO2 (P > 0.05; Table 3). Furthermore, elevated CO2 significantly decreased the foliar nitrogen content of resistant and susceptible cultivars of soybean at the R4 (Lamar: −16.20%; JLNMH: −8.15%) and R6 (Lamar: −15.81%; JLNMH: −10.14%) stages respectively (P < 0.05; Table 3). Finally, elevated CO2 significantly increased the seeds weight per plant of resistant soybean in 2013, 2014, and 2015 (+16.22, +26.01, and +15.87%), and of susceptible soybean just in 2014 (+21.26%) (P < 0.05; Fig. 1). Table 3. The growth and foliar chemistry of resistant (cv. Lamar) and susceptible (cv. JLNMH) cultivars of soybean during the R4 (i.e., full pods) and R6 (i.e., full seeds) stages grown under ambient and elevated CO2 from 2013 to 2015 (Mean ± SD) Stage  Treatment  Aboveground biomass (g/plant)  Belowground biomass (g/plant)  Root/shoot ratio (%)  Foliar sugar (%)  Foliar nitrogen (%)  C/N ratio  R4  eLamar  16.49 ± 1.49aB  3.29 ± 0.78  20.14 ± 5.34  4.13 ± 0.17aA  3.00 ± 0.34bB  1.39 ± 0.17aA  aLamar  13.71 ± 2.27bB  3.13 ± 0.63  23.46 ± 4.45A  3.25 ± 0.17bA  3.58 ± 0.39aB  0.92 ± 0.12bA  eJLNMH  20.99 ± 3.25aA  3.86 ± 0.45  18.59 ± 2.46  3.24 ± 0.13aB  4.28 ± 0.18bA  0.76 ± 0.04aB  aJLNMH  18.93 ± 1.41bA  3.56 ± 0.52  18.83 ± 2.65B  2.90 ± 0.16bB  4.66 ± 0.21aA  0.62 ± 0.05bB  R6  eLamar  25.49 ± 1.97aB  4.13 ± 0.92B  16.37 ± 4.17  3.57 ± 0.19aA  1.97 ± 0.17bB  1.82 ± 0.14aA  aLamar  21.70 ± 2.64bB  3.85 ± 0.59B  17.84 ± 2.49  2.94 ± 0.15bA  2.34 ± 0.16aB  1.25 ± 0.08bA  eJLNMH  35.39 ± 3.15aA  5.58 ± 0.35aA  15.60 ± 2.32  2.82 ± 0.13aB  3.19 ± 0.19bA  0.89 ± 0.06aB  aJLNMH  30.11 ± 2.79bA  4.80 ± 0.40bA  16.06 ± 1.98  2.58 ± 0.19bB  3.55 ± 0.30aA  0.73 ± 0.06bB  Stage  Treatment  Aboveground biomass (g/plant)  Belowground biomass (g/plant)  Root/shoot ratio (%)  Foliar sugar (%)  Foliar nitrogen (%)  C/N ratio  R4  eLamar  16.49 ± 1.49aB  3.29 ± 0.78  20.14 ± 5.34  4.13 ± 0.17aA  3.00 ± 0.34bB  1.39 ± 0.17aA  aLamar  13.71 ± 2.27bB  3.13 ± 0.63  23.46 ± 4.45A  3.25 ± 0.17bA  3.58 ± 0.39aB  0.92 ± 0.12bA  eJLNMH  20.99 ± 3.25aA  3.86 ± 0.45  18.59 ± 2.46  3.24 ± 0.13aB  4.28 ± 0.18bA  0.76 ± 0.04aB  aJLNMH  18.93 ± 1.41bA  3.56 ± 0.52  18.83 ± 2.65B  2.90 ± 0.16bB  4.66 ± 0.21aA  0.62 ± 0.05bB  R6  eLamar  25.49 ± 1.97aB  4.13 ± 0.92B  16.37 ± 4.17  3.57 ± 0.19aA  1.97 ± 0.17bB  1.82 ± 0.14aA  aLamar  21.70 ± 2.64bB  3.85 ± 0.59B  17.84 ± 2.49  2.94 ± 0.15bA  2.34 ± 0.16aB  1.25 ± 0.08bA  eJLNMH  35.39 ± 3.15aA  5.58 ± 0.35aA  15.60 ± 2.32  2.82 ± 0.13aB  3.19 ± 0.19bA  0.89 ± 0.06aB  aJLNMH  30.11 ± 2.79bA  4.80 ± 0.40bA  16.06 ± 1.98  2.58 ± 0.19bB  3.55 ± 0.30aA  0.73 ± 0.06bB  aLamar and eLamar–the soybean resistant cultivar (cv. Lamar) grown under ambient and elevated CO2, respectively; aJLNMH and eJLNMH–the soybean susceptible cultivar (cv. JLNMH) grown under ambient and elevated CO2, respectively. Different lowercase and uppercase letters indicates significant difference between ambient CO2 and elevated CO2 for same soybean cultivar, and between resistant and susceptible soybean cultivars grown under same CO2 level by Duncan’s test at P < 0.05. The same as in the Table 4. View Large Table 3. The growth and foliar chemistry of resistant (cv. Lamar) and susceptible (cv. JLNMH) cultivars of soybean during the R4 (i.e., full pods) and R6 (i.e., full seeds) stages grown under ambient and elevated CO2 from 2013 to 2015 (Mean ± SD) Stage  Treatment  Aboveground biomass (g/plant)  Belowground biomass (g/plant)  Root/shoot ratio (%)  Foliar sugar (%)  Foliar nitrogen (%)  C/N ratio  R4  eLamar  16.49 ± 1.49aB  3.29 ± 0.78  20.14 ± 5.34  4.13 ± 0.17aA  3.00 ± 0.34bB  1.39 ± 0.17aA  aLamar  13.71 ± 2.27bB  3.13 ± 0.63  23.46 ± 4.45A  3.25 ± 0.17bA  3.58 ± 0.39aB  0.92 ± 0.12bA  eJLNMH  20.99 ± 3.25aA  3.86 ± 0.45  18.59 ± 2.46  3.24 ± 0.13aB  4.28 ± 0.18bA  0.76 ± 0.04aB  aJLNMH  18.93 ± 1.41bA  3.56 ± 0.52  18.83 ± 2.65B  2.90 ± 0.16bB  4.66 ± 0.21aA  0.62 ± 0.05bB  R6  eLamar  25.49 ± 1.97aB  4.13 ± 0.92B  16.37 ± 4.17  3.57 ± 0.19aA  1.97 ± 0.17bB  1.82 ± 0.14aA  aLamar  21.70 ± 2.64bB  3.85 ± 0.59B  17.84 ± 2.49  2.94 ± 0.15bA  2.34 ± 0.16aB  1.25 ± 0.08bA  eJLNMH  35.39 ± 3.15aA  5.58 ± 0.35aA  15.60 ± 2.32  2.82 ± 0.13aB  3.19 ± 0.19bA  0.89 ± 0.06aB  aJLNMH  30.11 ± 2.79bA  4.80 ± 0.40bA  16.06 ± 1.98  2.58 ± 0.19bB  3.55 ± 0.30aA  0.73 ± 0.06bB  Stage  Treatment  Aboveground biomass (g/plant)  Belowground biomass (g/plant)  Root/shoot ratio (%)  Foliar sugar (%)  Foliar nitrogen (%)  C/N ratio  R4  eLamar  16.49 ± 1.49aB  3.29 ± 0.78  20.14 ± 5.34  4.13 ± 0.17aA  3.00 ± 0.34bB  1.39 ± 0.17aA  aLamar  13.71 ± 2.27bB  3.13 ± 0.63  23.46 ± 4.45A  3.25 ± 0.17bA  3.58 ± 0.39aB  0.92 ± 0.12bA  eJLNMH  20.99 ± 3.25aA  3.86 ± 0.45  18.59 ± 2.46  3.24 ± 0.13aB  4.28 ± 0.18bA  0.76 ± 0.04aB  aJLNMH  18.93 ± 1.41bA  3.56 ± 0.52  18.83 ± 2.65B  2.90 ± 0.16bB  4.66 ± 0.21aA  0.62 ± 0.05bB  R6  eLamar  25.49 ± 1.97aB  4.13 ± 0.92B  16.37 ± 4.17  3.57 ± 0.19aA  1.97 ± 0.17bB  1.82 ± 0.14aA  aLamar  21.70 ± 2.64bB  3.85 ± 0.59B  17.84 ± 2.49  2.94 ± 0.15bA  2.34 ± 0.16aB  1.25 ± 0.08bA  eJLNMH  35.39 ± 3.15aA  5.58 ± 0.35aA  15.60 ± 2.32  2.82 ± 0.13aB  3.19 ± 0.19bA  0.89 ± 0.06aB  aJLNMH  30.11 ± 2.79bA  4.80 ± 0.40bA  16.06 ± 1.98  2.58 ± 0.19bB  3.55 ± 0.30aA  0.73 ± 0.06bB  aLamar and eLamar–the soybean resistant cultivar (cv. Lamar) grown under ambient and elevated CO2, respectively; aJLNMH and eJLNMH–the soybean susceptible cultivar (cv. JLNMH) grown under ambient and elevated CO2, respectively. Different lowercase and uppercase letters indicates significant difference between ambient CO2 and elevated CO2 for same soybean cultivar, and between resistant and susceptible soybean cultivars grown under same CO2 level by Duncan’s test at P < 0.05. The same as in the Table 4. View Large Fig. 1. View largeDownload slide The seeds weight of resistant (cv. Lamar) and susceptible (cv. JLNMH) cultivars of soybean grown under ambient and elevated CO2 in 2013, 2014, and 2015. Each value represents the average (±SD). Different lowercase and uppercase letters indicated significant differences between ambient CO2 (aCO2) and elevated CO2 (eCO2) for same soybean cultivar, and between resistant and susceptible cultivars of soybean grown under same CO2 level by the Duncan’s test as P < 0.05, respectively. Fig. 1. View largeDownload slide The seeds weight of resistant (cv. Lamar) and susceptible (cv. JLNMH) cultivars of soybean grown under ambient and elevated CO2 in 2013, 2014, and 2015. Each value represents the average (±SD). Different lowercase and uppercase letters indicated significant differences between ambient CO2 (aCO2) and elevated CO2 (eCO2) for same soybean cultivar, and between resistant and susceptible cultivars of soybean grown under same CO2 level by the Duncan’s test as P < 0.05, respectively. The aboveground biomass and foliar nitrogen content of the resistant soybean were significantly lower than that of the susceptible soybean during the R4 (Ambient CO2: −27.58 and −23.18%; Elevated CO2: −21.44 and −29.91%) and R6 (Ambient CO2: −27.93 and −34.08%; Elevated CO2: −27.97 and −38.24%) stages respectively (P < 0.05; Table 3), and the belowground biomass of the resistant soybean was significantly lower than that of the susceptible soybean at the R6 stage (Ambient CO2: −19.79%; Elevated CO2: −24.50%) (P < 0.05; Table 3). Moreover, the root/shoot ratio of resistant soybean was significantly higher than that of the susceptible soybean at the R4 stage under ambient CO2 (+22.84%; P < 0.05; Table 3). Furthermore, the foliar sugar content and C/N ratio of resistant soybean were significantly higher than that of susceptible soybean at the R4 (Ambient CO2: +12.07 and +48.39%; Elevated CO2: +27.47 and +82.89%) and R6 (Ambient CO2: +13.95 and +72.60%; Elevated CO2: +26.60 and +104.49%) stages respectively (P < 0.05; Table 3). Finally, the seeds weight per plant of the resistant soybean was significantly higher than that of the susceptible soybean in 2013 (Ambient CO2: +112.77%; Elevated CO2: +142.05%), 2014 (Ambient CO2: +178.84%; Elevated CO2: +189.77%) and 2015 (Ambient CO2: +141.43%; Elevated CO2: +150.84%) respectively (P < 0.05; Fig. 1). Effects of Soybean Cultivar and Elevated CO2 on the Growth and Development, Reproduction, and Consumption of S. litura CO2 levels and soybean cultivars significantly affected the larval and pupal life span, larval and pupal weight, fecundity, feeding and excretion amount per larva, and net consumption per larva of S. litura (P < 0.001; Table 2). Moreover, there was a significant difference in the net consumption per larva among sampling years (P < 0.05; Table 2). Compared with ambient CO2, elevated CO2 significantly prolonged the larval life span of S. litura fed on resistant soybean (2013: +8.26%; 2014: +8.41%; 2015: +7.21%) and susceptible soybean (2014: +4.95%) (P < 0.05; Table 3), and significantly prolonged the pupal life span of S. litura fed on resistant soybean in 2014 (+6.45%) and 2015 (+6.45%) (P < 0.05; Table 4). Moreover, elevated CO2 significantly reduced the larval weight and fecundity of S. litura fed on resistant and susceptible soybean in 2013 (Lamar: −14.29% and −19.61%; JLNMH: −19.23% and −9.07%), 2014 (Lamar: −7.41% and −15.85%; JLNMH: −11.84% and −7.79%), and 2015 (Lamar: −7.27% and −11.95%; JLNMH: −15.58% and −12.26%) respectively (P < 0.05; Table 4), and significantly reduced the pupal weight of S. litura fed on resistant soybean (2014: −17.24%; 2015: −10.71%) and susceptible soybean (2014: −12.82%) (P < 0.05; Table 4). Furthermore, elevated CO2 significantly increased the feeding and excretion amount per larva of S. litura fed on resistant and susceptible soybean in 2013 (Lamar: +16.19 and +43.33%; JLNMH: +40.11 and +38.36%), 2014 (Lamar: +16.04 and +43.33%; JLNMH: +45.16 and +38.89%), and 2015 (Lamar: +16.82 and +45.16%; JLNMH: +47.59 and +33.33%) respectively (P < 0.05; Table 4), and significantly increased the net consumption per larva of S. litura fed on susceptible soybean in three sampling years (2013: +41.23%; 2014: +49.12%; 2015: +57.14%; P < 0.05; Table 4). Table 4. Effects of elevated CO2 on the growth, development and reproduction, feeding and excretion of S. litura fed on resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean grown under ambient and elevated CO2 in 2013–2015 (Mean ± SD) Year  Treatment  Larval life span (day)  Pupal life span (day)  Larval weight (g)  Pupal weight (g)  Fecundity (eggs laid/female)  Feeding amount (dry weight; g/larva)  Excretion amount (dry weight; g/larva)  Net consumption (dry weight; g/larva)  2013  eLamar  23.6 ± 0.55aA  13.4 ± 0.55aA  0.48 ± 0.03bB  0.25 ± 0.04aB  306.6 ± 60.7bB  1.22 ± 0.03aB  0.43 ± 0.02aB  0.79 ± 0.02aB  aLamar  21.8 ± 0.45bA  13.0 ± 0.71aA  0.56 ± 0.02aB  0.29 ± 0.02aB  381.4 ± 23.6aB  1.05 ± 0.06bB  0.30 ± 0.03bB  0.75 ± 0.03aB  eJLNMH  21.4 ± 0.55aB  10.8 ± 1.30aB  0.63 ± 0.03bA  0.35 ± 0.04aA  593.6 ± 17.2bA  2.62 ± 0.11aA  1.01 ± 0.05aA  1.61 ± 0.06aA  aJLNMH  20.6 ± 0.55aB  10.0 ± 0.71aB  0.78 ± 0.04aA  0.35 ± 0.03aA  652.8 ± 29.8aA  1.87 ± 0.06bA  0.73 ± 0.03bA  1.14 ± 0.03bA  2014  eLamar  23.2 ± 0.84aA  13.2 ± 0.45aA  0.50 ± 0.01bB  0.24 ± 0.03bB  342.0 ± 20.2bB  1.23 ± 0.13aB  0.43 ± 0.05aB  0.80 ± 0.08aB  aLamar  21.4 ± 0.55bA  12.4 ± 0.55bA  0.54 ± 0.02aB  0.29 ± 0.02aB  406.4 ± 30.9aB  1.06 ± 0.03bB  0.30 ± 0.01bB  0.77 ± 0.01aB  eJLNMH  21.2 ± 0.45aB  11.0 ± 1.22aB  0.67 ± 0.01bA  0.34 ± 0.02bA  572.6 ± 27.1bA  2.70 ± 0.02aA  1.00 ± 0.01aA  1.70 ± 0.01aA  aJLNMH  20.2 ± 0.84bB  9.8 ± 0.45aB  0.76 ± 0.02aA  0.39 ± 0.01aA  621.0 ± 30.2aA  1.86 ± 0.03bA  0.72 ± 0.01bA  1.14 ± 0.02bA  2015  eLamar  23.8 ± 0.45aA  13.2 ± 0.45aA  0.51 ± 0.04bB  0.25 ± 0.01bB  336.0 ± 19.8bB  1.25 ± 0.08aB  0.45 ± 0.04aB  0.80 ± 0.03aB  aLamar  22.2 ± 0.84bA  12.4 ± 0.55bA  0.55 ± 0.02aB  0.28 ± 0.02aB  381.6 ± 30.1aB  1.07 ± 0.07bB  0.31 ± 0.04bB  0.76 ± 0.03aB  eJLNMH  21.0 ± 0.71aB  11.4 ± 1.14aB  0.65 ± 0.04bA  0.35 ± 0.02aA  557.0 ± 26.8bA  2.76 ± 0.09aA  1.00 ± 0.04aA  1.76 ± 0.05aA  aJLNMH  20.8 ± 0.84aB  10.2 ± 1.10aB  0.77 ± 0.02aA  0.37 ± 0.04aA  634.8 ± 57.9aA  1.87 ± 0.04bA  0.75 ± 0.02bA  1.12 ± 0.02bA  Year  Treatment  Larval life span (day)  Pupal life span (day)  Larval weight (g)  Pupal weight (g)  Fecundity (eggs laid/female)  Feeding amount (dry weight; g/larva)  Excretion amount (dry weight; g/larva)  Net consumption (dry weight; g/larva)  2013  eLamar  23.6 ± 0.55aA  13.4 ± 0.55aA  0.48 ± 0.03bB  0.25 ± 0.04aB  306.6 ± 60.7bB  1.22 ± 0.03aB  0.43 ± 0.02aB  0.79 ± 0.02aB  aLamar  21.8 ± 0.45bA  13.0 ± 0.71aA  0.56 ± 0.02aB  0.29 ± 0.02aB  381.4 ± 23.6aB  1.05 ± 0.06bB  0.30 ± 0.03bB  0.75 ± 0.03aB  eJLNMH  21.4 ± 0.55aB  10.8 ± 1.30aB  0.63 ± 0.03bA  0.35 ± 0.04aA  593.6 ± 17.2bA  2.62 ± 0.11aA  1.01 ± 0.05aA  1.61 ± 0.06aA  aJLNMH  20.6 ± 0.55aB  10.0 ± 0.71aB  0.78 ± 0.04aA  0.35 ± 0.03aA  652.8 ± 29.8aA  1.87 ± 0.06bA  0.73 ± 0.03bA  1.14 ± 0.03bA  2014  eLamar  23.2 ± 0.84aA  13.2 ± 0.45aA  0.50 ± 0.01bB  0.24 ± 0.03bB  342.0 ± 20.2bB  1.23 ± 0.13aB  0.43 ± 0.05aB  0.80 ± 0.08aB  aLamar  21.4 ± 0.55bA  12.4 ± 0.55bA  0.54 ± 0.02aB  0.29 ± 0.02aB  406.4 ± 30.9aB  1.06 ± 0.03bB  0.30 ± 0.01bB  0.77 ± 0.01aB  eJLNMH  21.2 ± 0.45aB  11.0 ± 1.22aB  0.67 ± 0.01bA  0.34 ± 0.02bA  572.6 ± 27.1bA  2.70 ± 0.02aA  1.00 ± 0.01aA  1.70 ± 0.01aA  aJLNMH  20.2 ± 0.84bB  9.8 ± 0.45aB  0.76 ± 0.02aA  0.39 ± 0.01aA  621.0 ± 30.2aA  1.86 ± 0.03bA  0.72 ± 0.01bA  1.14 ± 0.02bA  2015  eLamar  23.8 ± 0.45aA  13.2 ± 0.45aA  0.51 ± 0.04bB  0.25 ± 0.01bB  336.0 ± 19.8bB  1.25 ± 0.08aB  0.45 ± 0.04aB  0.80 ± 0.03aB  aLamar  22.2 ± 0.84bA  12.4 ± 0.55bA  0.55 ± 0.02aB  0.28 ± 0.02aB  381.6 ± 30.1aB  1.07 ± 0.07bB  0.31 ± 0.04bB  0.76 ± 0.03aB  eJLNMH  21.0 ± 0.71aB  11.4 ± 1.14aB  0.65 ± 0.04bA  0.35 ± 0.02aA  557.0 ± 26.8bA  2.76 ± 0.09aA  1.00 ± 0.04aA  1.76 ± 0.05aA  aJLNMH  20.8 ± 0.84aB  10.2 ± 1.10aB  0.77 ± 0.02aA  0.37 ± 0.04aA  634.8 ± 57.9aA  1.87 ± 0.04bA  0.75 ± 0.02bA  1.12 ± 0.02bA  View Large Table 4. Effects of elevated CO2 on the growth, development and reproduction, feeding and excretion of S. litura fed on resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean grown under ambient and elevated CO2 in 2013–2015 (Mean ± SD) Year  Treatment  Larval life span (day)  Pupal life span (day)  Larval weight (g)  Pupal weight (g)  Fecundity (eggs laid/female)  Feeding amount (dry weight; g/larva)  Excretion amount (dry weight; g/larva)  Net consumption (dry weight; g/larva)  2013  eLamar  23.6 ± 0.55aA  13.4 ± 0.55aA  0.48 ± 0.03bB  0.25 ± 0.04aB  306.6 ± 60.7bB  1.22 ± 0.03aB  0.43 ± 0.02aB  0.79 ± 0.02aB  aLamar  21.8 ± 0.45bA  13.0 ± 0.71aA  0.56 ± 0.02aB  0.29 ± 0.02aB  381.4 ± 23.6aB  1.05 ± 0.06bB  0.30 ± 0.03bB  0.75 ± 0.03aB  eJLNMH  21.4 ± 0.55aB  10.8 ± 1.30aB  0.63 ± 0.03bA  0.35 ± 0.04aA  593.6 ± 17.2bA  2.62 ± 0.11aA  1.01 ± 0.05aA  1.61 ± 0.06aA  aJLNMH  20.6 ± 0.55aB  10.0 ± 0.71aB  0.78 ± 0.04aA  0.35 ± 0.03aA  652.8 ± 29.8aA  1.87 ± 0.06bA  0.73 ± 0.03bA  1.14 ± 0.03bA  2014  eLamar  23.2 ± 0.84aA  13.2 ± 0.45aA  0.50 ± 0.01bB  0.24 ± 0.03bB  342.0 ± 20.2bB  1.23 ± 0.13aB  0.43 ± 0.05aB  0.80 ± 0.08aB  aLamar  21.4 ± 0.55bA  12.4 ± 0.55bA  0.54 ± 0.02aB  0.29 ± 0.02aB  406.4 ± 30.9aB  1.06 ± 0.03bB  0.30 ± 0.01bB  0.77 ± 0.01aB  eJLNMH  21.2 ± 0.45aB  11.0 ± 1.22aB  0.67 ± 0.01bA  0.34 ± 0.02bA  572.6 ± 27.1bA  2.70 ± 0.02aA  1.00 ± 0.01aA  1.70 ± 0.01aA  aJLNMH  20.2 ± 0.84bB  9.8 ± 0.45aB  0.76 ± 0.02aA  0.39 ± 0.01aA  621.0 ± 30.2aA  1.86 ± 0.03bA  0.72 ± 0.01bA  1.14 ± 0.02bA  2015  eLamar  23.8 ± 0.45aA  13.2 ± 0.45aA  0.51 ± 0.04bB  0.25 ± 0.01bB  336.0 ± 19.8bB  1.25 ± 0.08aB  0.45 ± 0.04aB  0.80 ± 0.03aB  aLamar  22.2 ± 0.84bA  12.4 ± 0.55bA  0.55 ± 0.02aB  0.28 ± 0.02aB  381.6 ± 30.1aB  1.07 ± 0.07bB  0.31 ± 0.04bB  0.76 ± 0.03aB  eJLNMH  21.0 ± 0.71aB  11.4 ± 1.14aB  0.65 ± 0.04bA  0.35 ± 0.02aA  557.0 ± 26.8bA  2.76 ± 0.09aA  1.00 ± 0.04aA  1.76 ± 0.05aA  aJLNMH  20.8 ± 0.84aB  10.2 ± 1.10aB  0.77 ± 0.02aA  0.37 ± 0.04aA  634.8 ± 57.9aA  1.87 ± 0.04bA  0.75 ± 0.02bA  1.12 ± 0.02bA  Year  Treatment  Larval life span (day)  Pupal life span (day)  Larval weight (g)  Pupal weight (g)  Fecundity (eggs laid/female)  Feeding amount (dry weight; g/larva)  Excretion amount (dry weight; g/larva)  Net consumption (dry weight; g/larva)  2013  eLamar  23.6 ± 0.55aA  13.4 ± 0.55aA  0.48 ± 0.03bB  0.25 ± 0.04aB  306.6 ± 60.7bB  1.22 ± 0.03aB  0.43 ± 0.02aB  0.79 ± 0.02aB  aLamar  21.8 ± 0.45bA  13.0 ± 0.71aA  0.56 ± 0.02aB  0.29 ± 0.02aB  381.4 ± 23.6aB  1.05 ± 0.06bB  0.30 ± 0.03bB  0.75 ± 0.03aB  eJLNMH  21.4 ± 0.55aB  10.8 ± 1.30aB  0.63 ± 0.03bA  0.35 ± 0.04aA  593.6 ± 17.2bA  2.62 ± 0.11aA  1.01 ± 0.05aA  1.61 ± 0.06aA  aJLNMH  20.6 ± 0.55aB  10.0 ± 0.71aB  0.78 ± 0.04aA  0.35 ± 0.03aA  652.8 ± 29.8aA  1.87 ± 0.06bA  0.73 ± 0.03bA  1.14 ± 0.03bA  2014  eLamar  23.2 ± 0.84aA  13.2 ± 0.45aA  0.50 ± 0.01bB  0.24 ± 0.03bB  342.0 ± 20.2bB  1.23 ± 0.13aB  0.43 ± 0.05aB  0.80 ± 0.08aB  aLamar  21.4 ± 0.55bA  12.4 ± 0.55bA  0.54 ± 0.02aB  0.29 ± 0.02aB  406.4 ± 30.9aB  1.06 ± 0.03bB  0.30 ± 0.01bB  0.77 ± 0.01aB  eJLNMH  21.2 ± 0.45aB  11.0 ± 1.22aB  0.67 ± 0.01bA  0.34 ± 0.02bA  572.6 ± 27.1bA  2.70 ± 0.02aA  1.00 ± 0.01aA  1.70 ± 0.01aA  aJLNMH  20.2 ± 0.84bB  9.8 ± 0.45aB  0.76 ± 0.02aA  0.39 ± 0.01aA  621.0 ± 30.2aA  1.86 ± 0.03bA  0.72 ± 0.01bA  1.14 ± 0.02bA  2015  eLamar  23.8 ± 0.45aA  13.2 ± 0.45aA  0.51 ± 0.04bB  0.25 ± 0.01bB  336.0 ± 19.8bB  1.25 ± 0.08aB  0.45 ± 0.04aB  0.80 ± 0.03aB  aLamar  22.2 ± 0.84bA  12.4 ± 0.55bA  0.55 ± 0.02aB  0.28 ± 0.02aB  381.6 ± 30.1aB  1.07 ± 0.07bB  0.31 ± 0.04bB  0.76 ± 0.03aB  eJLNMH  21.0 ± 0.71aB  11.4 ± 1.14aB  0.65 ± 0.04bA  0.35 ± 0.02aA  557.0 ± 26.8bA  2.76 ± 0.09aA  1.00 ± 0.04aA  1.76 ± 0.05aA  aJLNMH  20.8 ± 0.84aB  10.2 ± 1.10aB  0.77 ± 0.02aA  0.37 ± 0.04aA  634.8 ± 57.9aA  1.87 ± 0.04bA  0.75 ± 0.02bA  1.12 ± 0.02bA  View Large Compared with susceptible soybean, resistant soybean significantly prolonged the larval and pupal life span of S. litura in 2013 (Ambient CO2: +5.83 and +30.00%; Elevated CO2: +10.28 and +24.07%), 2014 (Ambient CO2: +5.94 and +26.53%; Elevated CO2: +9.43 and +20.00%), and 2015 (Ambient CO2: +6.73 and +21.57%; Elevated CO2: +13.33 and +15.79%) respectively (P < 0.05; Table 4), and significantly reduced the larval and pupal weight, fecundity, feeding and excretion amount per larva, and net consumption per larva of S. litura in 2013 (Ambient CO2: −28.21, −17.14, −41.57, −43.85, −58.90, and −34.21%; Elevated CO2: −23.81, −28.57, −48.35, −53.44, −57.43, and −50.93%), 2014 (Ambient CO2: −28.95, −25.64, −34.56, −43.01, −58.33, and −32.46%; Elevated CO2: −25.37, −29.41, −40.27, −54.44, −57.00, and −52.94%), and 2015 (Ambient CO2: −28.57, −24.32, −39.89, −42.78, −58.67, and −32.14%; Elevated CO2: −21.54, −28.57, −39.68, −54.71, −55.00, and −54.55%) respectively (P < 0.05; Table 4). Effects of the Interaction Between Soybean Cultivar and CO2 Concentration on the Foliar Chemistry and Yield of Soybean The foliar sugar content and C/N ratio at R4 and R6 stages of soybean (P < 0.01 or 0.001; Table 2), and the seeds weight per plant (P < 0.001; Table 2) were significantly affected by the interaction between CO2 levels and soybean cultivars. Moreover, there was a significant interaction between sampling years and soybean cultivars on the seeds weight per plant (P < 0.05; Table 2). Although the foliar sugar content and C/N ratio of resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean cultivars increased with elevated CO2. However, there was a significant difference in the increment, foliar sugar content in eLamar compared with aLamar increased more than that of eJLNMH compared with aJLNMH, and the increment was more than twice both at R4 (+131.06%) and R6 (+130.43%) stages, similar difference was also found in C/N ratio (R4: +126.26%; R6: +102.74%) (Table 3). Moreover, the seeds weight per plant of eLamar increased significantly in the three sampling years, but the increase of eJLNMH was not so obvious, just in 2014 increased significantly (Fig. 1). Effects of the Interaction Between Soybean Cultivar and CO2 Concentration on the Growth, Development, and Consumption of S. litura The larval life span, larval weight, feeding and excretion amount per larva, and net consumption per larva were significantly affected by the interaction between CO2 levels and soybean cultivars (P < 0.01 or 0.001; Table 2). Moreover, there was significant interaction between sampling years and CO2 levels on the larval weight (P < 0.05; Table 2) and net consumption per larva (P < 0.01; Table 2), and there was significant interaction between sampling years and soybean cultivars on the fecundity (P < 0.05; Table 2), and there was significant interaction among sampling years, CO2 levels, and soybean cultivars on the net consumption (P < 0.01; Table 2). The larval life span of S. litura fed on eLamar was significantly prolonged compared with aLamar in the three sampling years, but the larval life span of S. litura fed on eJLNMH was significantly prolonged compared with aJLNMH just in 2014, and the decrement of larval weight fed on eLamar was less than 25% of the decrement of S. litura fed on eJLNMH in the three sampling years (2013: −25.69%; 2014: −37.42%; 2015: −53.34%) (Table 4). Moreover, the increment of feeding amount per larva of S. litura fed on eLamar was less than 50% of the increment of S. litura fed on eJLNMH in the three sampling years (2013: −59.64%; 2014: −64.48%; 2015: −64.66%), and the increment of excretion amount per larva of S. litura fed on eLamar was more than 10% of the increment of S. litura fed on eJLNMH in the three sampling years (2013: +12.96%; 2014: +11.42%; 2015: +35.49%) (Table 4). Furthermore, the net consumption of S. litura fed on eLamar was insignificant compared with aLamar in the three sampling years, but the eJLNMH significantly increased more than 40% compared with aJLNMH in the three sampling years (Table 4). Correlation Analysis Between the Foliar Chemistry of Soybean and the Growth Indexes of S. litura in Different of CO2 Levels and Sampling Years The foliar sugar content of resistant soybean Lamar and susceptible soybean JLNMH in different of CO2 levels (elevated vs. ambient) and sampling years (2013, 2014, and 2015) was significantly positive correlated with the foliar C/N ratio of soybean, the larval and pupal life span, feeding and excretion amount per larva, and net consumption per larva of S. litura, and was significantly negative correlated with the foliar N content of soybean, the larval weight, pupal weight (except susceptible soybean JLNMH), and fecundity of S. litura (Table 5). The correlation between the foliar C/N ratio of soybean and the growth indexes of S. litura was similar to that of the foliar sugar content and the growth indexes of S. litura (Table 5). The correlation between the foliar N content of soybean and the growth indexes of S. litura was opposite with the first two (Table 5). Table 5. Correlation analysis between the measured indexes of foliar chemistry of soybean and the growth of S. litura fed on resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean grown under ambient and elevated CO2 in 2013, 2014 and 2015 Correlation analysis  Foliar sugar  Foliar nitrogen  Foliar C/N ratio  Larval life span  Pupal life span  Larval weight  Pupal weight  Fecundity  Feeding amount  Excretion amount  Net consumption  Foliar sugar    −0.98‡  0.99‡  0.92†  0.81*  −0.93†  −0.99‡  −0.88*  0.98‡  0.98‡  0.96†  Foliar nitrogen  −0.96†    −0.99‡  −0.96†  −0.87*  0.89*  0.99‡  0.93†  −0.97†  −0.98‡  −0.90*  Foliar C/N ratio  0.99‡  −0.99‡    0.94†  0.85*  −0.90*  −0.99‡  −0.89*  0.98‡  0.98‡  0.94†  Larval life span  0.84*  −0.94†  0.90*    0.81  −0.86*  −0.94†  −0.94†  0.96†  0.98‡  0.86*  Pupal life span  0.94†  −0.93†  0.95†  0.79    −0.74  −0.80  −0.89*  0.80  0.82*  0.67  Larval weight  −0.98‡  0.91*  −0.95†  −0.83*  −0.88*    0.92†  0.89*  −0.92*  −0.91*  −0.90*  Pupal weight  −0.61  0.76  −0.72  −0.74  −0.65  0.54    0.90*  −0.98‡  −0.98‡  −0.94†  Fecundity  −0.93†  0.82*  −0.88*  −0.61  −0.92*  0.88*  0.40    −0.88*  −0.91*  −0.75  Feeding amount  1.00‡  −0.96†  0.99‡  0.82*  0.96†  −0.96†  −0.66  −0.93†    1.00‡  0.97†  Excretion amount  1.00‡  −0.97†  0.99‡  0.88*  0.93†  −0.98‡  −0.67  −0.89*  0.99‡    0.94†  Net consumption  0.99‡  −0.94†  0.98‡  0.78  0.96†  −0.95†  −0.65  −0.95†  1.00‡  0.98‡    Correlation analysis  Foliar sugar  Foliar nitrogen  Foliar C/N ratio  Larval life span  Pupal life span  Larval weight  Pupal weight  Fecundity  Feeding amount  Excretion amount  Net consumption  Foliar sugar    −0.98‡  0.99‡  0.92†  0.81*  −0.93†  −0.99‡  −0.88*  0.98‡  0.98‡  0.96†  Foliar nitrogen  −0.96†    −0.99‡  −0.96†  −0.87*  0.89*  0.99‡  0.93†  −0.97†  −0.98‡  −0.90*  Foliar C/N ratio  0.99‡  −0.99‡    0.94†  0.85*  −0.90*  −0.99‡  −0.89*  0.98‡  0.98‡  0.94†  Larval life span  0.84*  −0.94†  0.90*    0.81  −0.86*  −0.94†  −0.94†  0.96†  0.98‡  0.86*  Pupal life span  0.94†  −0.93†  0.95†  0.79    −0.74  −0.80  −0.89*  0.80  0.82*  0.67  Larval weight  −0.98‡  0.91*  −0.95†  −0.83*  −0.88*    0.92†  0.89*  −0.92*  −0.91*  −0.90*  Pupal weight  −0.61  0.76  −0.72  −0.74  −0.65  0.54    0.90*  −0.98‡  −0.98‡  −0.94†  Fecundity  −0.93†  0.82*  −0.88*  −0.61  −0.92*  0.88*  0.40    −0.88*  −0.91*  −0.75  Feeding amount  1.00‡  −0.96†  0.99‡  0.82*  0.96†  −0.96†  −0.66  −0.93†    1.00‡  0.97†  Excretion amount  1.00‡  −0.97†  0.99‡  0.88*  0.93†  −0.98‡  −0.67  −0.89*  0.99‡    0.94†  Net consumption  0.99‡  −0.94†  0.98‡  0.78  0.96†  −0.95†  −0.65  −0.95†  1.00‡  0.98‡    Foliar sugar and N contents, and C/N ratio are average of R4 and R6 stages in the same year for the same CO2 level. The right triangle (and the left triangle) is the correlation analysis between the measured indexes of foliar chemistry of resistant soybean Lamar (and susceptible soybean JLNMH) and the growth of S. litura in different of CO2 levels (elevated vs. ambient) and sampling years (2013, 2014, and 2015). Pearson correlation coefficient, N = 6; Prob > |r| under H0: Rho = 0. *P < 0.05, †P < 0.01, ‡P < 0.001. View Large Table 5. Correlation analysis between the measured indexes of foliar chemistry of soybean and the growth of S. litura fed on resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean grown under ambient and elevated CO2 in 2013, 2014 and 2015 Correlation analysis  Foliar sugar  Foliar nitrogen  Foliar C/N ratio  Larval life span  Pupal life span  Larval weight  Pupal weight  Fecundity  Feeding amount  Excretion amount  Net consumption  Foliar sugar    −0.98‡  0.99‡  0.92†  0.81*  −0.93†  −0.99‡  −0.88*  0.98‡  0.98‡  0.96†  Foliar nitrogen  −0.96†    −0.99‡  −0.96†  −0.87*  0.89*  0.99‡  0.93†  −0.97†  −0.98‡  −0.90*  Foliar C/N ratio  0.99‡  −0.99‡    0.94†  0.85*  −0.90*  −0.99‡  −0.89*  0.98‡  0.98‡  0.94†  Larval life span  0.84*  −0.94†  0.90*    0.81  −0.86*  −0.94†  −0.94†  0.96†  0.98‡  0.86*  Pupal life span  0.94†  −0.93†  0.95†  0.79    −0.74  −0.80  −0.89*  0.80  0.82*  0.67  Larval weight  −0.98‡  0.91*  −0.95†  −0.83*  −0.88*    0.92†  0.89*  −0.92*  −0.91*  −0.90*  Pupal weight  −0.61  0.76  −0.72  −0.74  −0.65  0.54    0.90*  −0.98‡  −0.98‡  −0.94†  Fecundity  −0.93†  0.82*  −0.88*  −0.61  −0.92*  0.88*  0.40    −0.88*  −0.91*  −0.75  Feeding amount  1.00‡  −0.96†  0.99‡  0.82*  0.96†  −0.96†  −0.66  −0.93†    1.00‡  0.97†  Excretion amount  1.00‡  −0.97†  0.99‡  0.88*  0.93†  −0.98‡  −0.67  −0.89*  0.99‡    0.94†  Net consumption  0.99‡  −0.94†  0.98‡  0.78  0.96†  −0.95†  −0.65  −0.95†  1.00‡  0.98‡    Correlation analysis  Foliar sugar  Foliar nitrogen  Foliar C/N ratio  Larval life span  Pupal life span  Larval weight  Pupal weight  Fecundity  Feeding amount  Excretion amount  Net consumption  Foliar sugar    −0.98‡  0.99‡  0.92†  0.81*  −0.93†  −0.99‡  −0.88*  0.98‡  0.98‡  0.96†  Foliar nitrogen  −0.96†    −0.99‡  −0.96†  −0.87*  0.89*  0.99‡  0.93†  −0.97†  −0.98‡  −0.90*  Foliar C/N ratio  0.99‡  −0.99‡    0.94†  0.85*  −0.90*  −0.99‡  −0.89*  0.98‡  0.98‡  0.94†  Larval life span  0.84*  −0.94†  0.90*    0.81  −0.86*  −0.94†  −0.94†  0.96†  0.98‡  0.86*  Pupal life span  0.94†  −0.93†  0.95†  0.79    −0.74  −0.80  −0.89*  0.80  0.82*  0.67  Larval weight  −0.98‡  0.91*  −0.95†  −0.83*  −0.88*    0.92†  0.89*  −0.92*  −0.91*  −0.90*  Pupal weight  −0.61  0.76  −0.72  −0.74  −0.65  0.54    0.90*  −0.98‡  −0.98‡  −0.94†  Fecundity  −0.93†  0.82*  −0.88*  −0.61  −0.92*  0.88*  0.40    −0.88*  −0.91*  −0.75  Feeding amount  1.00‡  −0.96†  0.99‡  0.82*  0.96†  −0.96†  −0.66  −0.93†    1.00‡  0.97†  Excretion amount  1.00‡  −0.97†  0.99‡  0.88*  0.93†  −0.98‡  −0.67  −0.89*  0.99‡    0.94†  Net consumption  0.99‡  −0.94†  0.98‡  0.78  0.96†  −0.95†  −0.65  −0.95†  1.00‡  0.98‡    Foliar sugar and N contents, and C/N ratio are average of R4 and R6 stages in the same year for the same CO2 level. The right triangle (and the left triangle) is the correlation analysis between the measured indexes of foliar chemistry of resistant soybean Lamar (and susceptible soybean JLNMH) and the growth of S. litura in different of CO2 levels (elevated vs. ambient) and sampling years (2013, 2014, and 2015). Pearson correlation coefficient, N = 6; Prob > |r| under H0: Rho = 0. *P < 0.05, †P < 0.01, ‡P < 0.001. View Large Discussion Effects of Elevated CO2 on Resistant and Susceptible Soybean Elevated CO2 caused increase in aboveground biomass, foliar sugar content and C/N ratio, and reduction in root/shoot ratio (but not significant) and foliar nitrogen content in both resistant and susceptible soybean, confirming the results of other studies (Poorter 1993, Johns and Hughes 2002, Chen et al. 2005). In general, the present atmospheric CO2 concentration is unsaturated for plant photosynthesis (Su et al. 2016). In theory, the increase of atmospheric CO2 concentration has a ‘fertilizer effect’ on plant growth, especially photosynthesis and productivity of the C3 plants (such as wheat, rice, soybean, cotton, etc.) can be improved by the fertilizer effect (Rogers and Dahlman 1993, Rogers et al. 1994), which is conducive to plant growth. Accumulation of nonstructural carbohydrates increased foliar sugars and the C/N ratio and simultaneously decreased foliar N under elevated CO2 (Kimball et al. 1994, Lindroth et al. 1995). The seeds weight of resistant soybean Lamar increased significantly in the three sampling years under elevated CO2, but the increase of susceptible soybean JLNMH was not so obvious. Moreover, the interaction between CO2 levels and soybean cultivars had significant effects on the sugar content and C/N ratio. Foliar sugar content in soybean Lamar increased more than that of the susceptible soybean JLNMH under elevated CO2, and the increment was more than twice, similar difference was also found in C/N ratio. These differences between the resistant soybean and susceptible soybean may due to the characteristics of PI229358 soybean, Tester (1977) found that the resistant soybean (PI229358) had equivalent soluble carbohydrates and 33% more than the susceptible cultivars, the susceptible cultivars accumulated more total nitrogen and at a faster rate than did the resistant plant introductions. Effects of Resistant Soybean Grown Under Elevated CO2 on the Growth, Development, and Reproduction of S. litura Most herbivorous insects appear to be negatively affected by elevated CO2 because of the reduction in foliar N and increase in foliar C/N ratio (Roth and Lindroth 1995, Ji et al. 2011). According to the analysis of the correlation between foliar chemistry of soybean and the growth indexes of S. litura under elevated CO2 and ambient CO2 and in sampling years (2013, 2014, and 2015), high foliar sugar and low N content, and high foliar C/N ratio were found to be negative to the growth, development, and fecundity of S. litura. The elevated CO2 was confirmed to affect the foliar nutrition of soybean, and then to affect the growth and development of S. litura. Based on the ‘Nutrition compensation hypothesis (NH)’ (Nicolas and Sillans 1989, Pennings et al. 1993), elevated CO2 can indirectly affect the development fitness of herbivores by changing the nutritional components of foliar C/N ratio, above-and belowground biomass, and photosynthetic rate of host plants (Ainsworth and Rogers 2007, Jackson et al. 2009, Zavala et al. 2013). Because nitrogen is the most important limiting resource for phytophagous insects (Mattson 1980), so nitrogen content limits insect growth and development. The reduction in food quality might cause the higher feeding of larvae because of the reduction in protein contents, and the higher foliar C/N ratio under elevated CO2 (Hunter 2001). In this study, 21.92~51.09% increase in foliar C/N ratio, and 8.15~16.20% decrease in N content was observed under elevated CO2, which affected the growth and development of S. litura, increased the consumption and fecal matter, prolonged the life span, reduced the weight and moth fecundity. This is consistent with most of the previous studies (Goverde and Erhardt 2002, Johns and Hughes 2002). In addition, the net consumption of S. litura fed on resistant soybean was insignificant between elevated and ambient CO2, while the susceptible soybean significantly increased more than 40% in elevated CO2 compared with ambient CO2. Moreover, the increment of feeding and excretion amount per larva of S. litura fed on resistant soybean were less than 50% and more than 10% of the increments of S. litura fed on susceptible soybean under elevated CO2. Furthermore, the larval life span of S. litura fed on resistant soybean (cv. Lamar) was prolonged more obvious than that of S. litura fed on susceptible soybean (cv. JLNMH) under elevated CO2. Elden and Kenworthy (1994) found that forliar P content of PI229358 soybean was significantly lower than that of some susceptible soybean, according to the ‘Growth rate hypothesis (GRH)’ (Elser et al. 2003), the change of C: N: P ratio was mainly decided by the changes of P content in organisms (Elser et al. 2000, Vanni et al. 2002), low P content of the host plant tissues would limit the growth and development of herbivorous insect (Schade et al. 2003). Besides, when herbivorous insects fed low favorite food, their consumption decreased and developmental duration was prolonged (Zhu et al. 2005, Zhang et al. 2018). As expected, there was significant year-to-year variation in our field research data. Nevertheless, the study exemplifies the complexities of predicting herbivore responses to future climate conditions, particularly in combination with the highly resistant soybean cultivar. The results clearly indicate that elevated CO2 had promoted the biomass and yield of soybean crops, and had negative effects on development of S. litura. This study supports our hypothesis, it seems that the resistant soybean (cv. Lamar) is likely better in yield performance under the increase of carbon dioxide concentration in the future than the susceptible cultivar JLNMH. Moreover, the resistant soybean (cv. Lamar) seems more adaptable to the future concentration of CO2, embodied in better performance against herbivorous Lepidoptera insect pests feeding with the plant chemistry change. About the improvement of the resistance in cultivar Lamar, we speculate that it might be the difference in the plant secondary metabolites of resistant soybean under elevated CO2, which needs further substantiation. Acknowledgments This research was funded and financially supported by National Key Research and Development Program of China (2017YFD0200400, 2016YFD0100201-22), National Natural Science Foundation of China (ID 31571694, 31272051), the Program for Changjiang Scholars and Innovative Research Team in University (ID PCSIRT_17R55), supported by the Fundamental Research Funds for the Central Universities (ID KYT201801), the Natural Science Foundation of Jiangsu Province Youth Fund (SBK2016043525), the Research Grant from the Innovation Project for Graduate Student of Jiangsu Province (KYLX16-1059), the Innovation Training Program for College Student of Jiangsu Province (201710307006X). References Cited Aldea, M., J. G. Hamilton, J. P. Resti, A. R. Zangerl, M. R. Berenbaum, and E. H. D. Elucia. 2005. Indirect effects of insect herbivory on leaf gas exchange in soybean. Plant. Cell Environ . 28: 402– 411. Google Scholar CrossRef Search ADS   Ainsworth, E. A., and S. P. Long. 2005. What have we learned from 15 years of free-air CO2 enrichment (FACE)? A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO2. New Phytol . 165: 351– 371. Google Scholar CrossRef Search ADS PubMed  Ainsworth, E. A., and A. Rogers. 2007. The response of photosynthesis and stomatal conductance to rising [CO2]: mechanisms and environmental interactions. Plant. Cell Environ . 30: 258– 270. Google Scholar CrossRef Search ADS PubMed  Ainsworth, E. A., A. Rogers, A. D. Leakey, L. E. Heady, Y. Gibon, M. Stitt, and U. Schurr. 2007. Does elevated atmospheric [CO2] alter diurnal C uptake and the balance of C and N metabolites in growing and fully expanded soybean leaves? J. Exp. Bot . 58: 579– 591. Google Scholar CrossRef Search ADS PubMed  Ainsworth, E. A., C. R. Yendrek, S. Sitch, W. J. Collins, and L. D. Emberson. 2012a. The effects of tropospheric ozone on net primary productivity and implications for climate change. Annu. Rev. Plant Biol . 63: 637– 661. Google Scholar CrossRef Search ADS   Ainsworth, E. A., C. R. Yendrek, J. A. Skoneczka, and S. P. Long. 2012b. Accelerating yield potential in soybean: potential targets for biotechnological improvement. Plant. Cell Environ . 35: 38– 52. Google Scholar CrossRef Search ADS   Armes, N. J., J. A. Wightman, D. R. Jadhav, and G. V. R. Rao. 1997. Status of insecticide resistance in Spodoptera litura in Andhra Pradesh, India. Pestic. Sci . 50: 240– 248. Google Scholar CrossRef Search ADS   Bazzaz, F. A. 1990. The responses of natural ecosystems to the rising global CO2 levels. Annu. Rev. Ecol. Syst . 21: 167– 196. Google Scholar CrossRef Search ADS   Casteel, C. L., O. K. Niziolek, A. D. B. Leakey, M. R. Berenbaum, and E. H. Delucia. 2012. Effects of elevated CO2, and soil water content on phytohormone transcript induction in Glycine max, after Popillia japonica, feeding. Arthropod Plant Interact . 6: 439– 447. Google Scholar CrossRef Search ADS   Chen, F. J., and F. Ge. 2004. A climatic chamber for controlling CO2 concentration- CDCC-1 chamber. Entomol. Knowledg . 41: 279– 281. Chen, F. J., G. Wu, F. Ge, M. N. Parajulee, and R. B. Shrestha. 2005. Effects of elevated CO2 and transgenic Bt cotton on plant chemistry, performance, and feeding of an insect herbivore, the cotton bollworm. Entomol. Exp. Appl . 115: 341– 350. Google Scholar CrossRef Search ADS   Chen, F. J., Z. H. Dang, and G. J. Wan. 2011. An open-top chamber and experimental facility suitable for simulating the greenhouse effect: China. 201120042889, 1[P]. Chen, X., B. Vosman, R. G. Visser, R. A. van der Vlugt, and C. Broekgaarden. 2012. High throughput phenotyping for aphid resistance in large plant collections. Plant Methods . 8: 33. Google Scholar CrossRef Search ADS PubMed  Coley, P. D. 1998. Possible effects of climate change on plant/ herbivore interactions in moist tropical forests. Clim. Change  39: 455– 472. Google Scholar CrossRef Search ADS   Deng, X. Y., X. C. Wang, W. Y. Yang, and Q. Zhang. 2012. Effect of nitrogen strategies on carbon and nitrogen metabolism of maize in wheat/maize/soybean relay intercropping system. Acta Prataculture Sinica . 21: 52– 61. Deng, P., W. H. Ma, and G. Q. Li. 2015. Age-and nutrition-related cannibalism in larvae of the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae). Acta Entomologica Sinica . 58: 175– 180. Drake, B. G., M. A. Gonzalez-Meler, and S. P. Long. 1997. More efficient plants: a consequence of rising atmospheric CO2? Annu. Rev. Plant Physiol. Plant Mol. Biol . 48: 609– 639. Google Scholar CrossRef Search ADS PubMed  Elden, T. C., and W. J. Kenworthy. 1994. Foliar nutrient concentrations of insect susceptible and resistant soybean germplasm. Corp Sci . 34: 695– 699. Google Scholar CrossRef Search ADS   Elser, J. J., W. F. Fagan, R. F. Denno, D. R. Dobberfuhl, A. Folarin, A. Huberty, S. Interlandi, S. S. Kilham, E. McCauley, K. L. Schulz,et al.   2000. Nutritional constraints in terrestrial and freshwater food webs. Nature  408: 578– 580. Google Scholar CrossRef Search ADS PubMed  Elser, J. J., K. Acharya, M. Kyle, J. Cotner, W. Makino, T. Markow, T. Watts, S. Hobbie, W. Fagan, J. Schade, J. Hood, and R. W. Sterner. 2003. Growth rate–stoichiometry couplings in diverse biota. Ecol. Lett . 6: 936– 943. Google Scholar CrossRef Search ADS   EMBRAPA. Centro Nacional de Pesquisa de Solos. 2009. Manual de métodos analyses químicas para avaliação de fertilidade do solo , 2nd ed. Embrapa Informações Tecnológicas, Brasília, Brazil, 627p. Fehr, W. R., C. E. Caviness, D. T. Burmood, and J. S. Pennington. 1971. Stage of development descriptions for soybeans, Glycine max (L.) Merrill. Crop Sci . 11: 929– 931. Google Scholar CrossRef Search ADS   Goverde, M., and A. Erhardt. 2002. Effects of elevated CO2 on development and larval food-preference in the butterfly coenonympha pamphuis (Lepidoptera, Satyridae). Glob. Chang. Biol . 9: 74– 83. Google Scholar CrossRef Search ADS   Hamilton, J. G., O. Dermody, M. Aldea, A. R. Zangerl, A. Rogers, M. R. Berenbaum, and E. H. Delucia. 2005. Anthropogenic changes in tropospheric composition increase susceptibility of soybean to insect herbivory. Environ. Entomol . 34: 479– 485. Google Scholar CrossRef Search ADS   Hartwig, E. E., L. Lambent, and T. C. Kilen. 1990. Registration of soybean cultivar Lamar. Crop Sci . 30: 231. Horie, T., J. T. Baker, and H. Nakagawa. 2000. Crop ecosystem responses to climatic change: rice, pp. 81– 106. In K. R. Reddy and H. F. Hodges (eds.), Climate change and global crop productivity . CABI publishing, Wallingford, United Kingdom. Google Scholar CrossRef Search ADS   Houghton, J. T., Y. Ding, D. J. Griggs, M. Noquer, P. J. van der Linden, and D. Xiaosu. 2001. Climate change 2001: the scientific basis . Cambridge University Press, Cambridge, United Kingdom. Hunter, M. D. 2001. Effects of elevated atmospheric carbon dioxide on insect-plant interactions. Agric. Forest Entomol . 3: 153– 159. Google Scholar CrossRef Search ADS   IPCC. 2014. Impacts, adaptation and vulnerability. Working group II contribution to the fifth assessment report of the intergovernmental panel on climate change, 1132. In C. B. Field, V. R. Barros, D. J. Dokken, K. J. Mach, M. D. Mastrandrea, T. E. Bilir, M. Chatterjee, K. L. Ebi, Y. O. Estrada, R. C. Genova, B. Girma, E. S. Kissel, A. N. Levy, S. MacCracken, P. R. Mastrandrea & L. L. White (eds.). Cambridge, UK: Cambridge University Press. Jackson, R. B., C. W. Cook, J. S. Pippen, and S. M. Palmer. 2009. Increased belowground biomass and soil CO2 fluxes after a decade of carbon dioxide enrichment in a warm-temperate forest. Ecology  90: 3352– 3366. Google Scholar CrossRef Search ADS PubMed  Ji, L. Z., L. L. An, and X. W. Wang. 2011. Growth responses of gypsy moth larvae to elevated CO2: the influence of methods of insect rearing. Insect Sci . 18: 409– 418. Google Scholar CrossRef Search ADS   Johns, C. V., and L. Hughes. 2002. Interactive effects of elevated CO2 and temperature on the leaf-miner Dialectica scalariella Zeller (Lepidoptera: Gracillariidae) in Paterson’s Curse, Echium plantagineum (Boraginaceae). Glob. Chang. Biol . 8: 142– 152. Google Scholar CrossRef Search ADS   Kim, H. Y., M. Lieffering, K. Kobayashi, M. Okada, and M. Shu. 2003. Seasonal changes in the effects of elevated CO2 on rice at three levels of nitrogen supply: a free air CO2 enrichment (face) experiment. Glob. Chang. Biol . 9: 826– 837. Google Scholar CrossRef Search ADS   Kimball, B. A., R. L. Lamorte, R. S. Seay, P. J. Pinter, R. Rokey, D. J. Hunsaker, W. A. Dugas, M. L. Heuer, J. R. Mauney, G. R. Hendrey,et al.   1994. Effects of free-air CO2-enrichment on energy balance and evapotranspiration of cotton. Agric. For. Meteorol . 70: 259– 278. Google Scholar CrossRef Search ADS   Kimball, B. A., K. Kobayashi, and M. Bindi. 2002. Responses of agricultural crops to free-air CO2 enrichment. Adv. Agron . 77: 293– 368. Google Scholar CrossRef Search ADS   Lambert, L., and T. C. Kilen. 1984. Multiple insect resistance in several soybean genotypes. Crop Sci . 24: 887– 890. Google Scholar CrossRef Search ADS   Lindroth, R. L. 2010. Impacts of elevated atmospheric CO2 and O3 on forests: phytochemistry, trophic interactions, and ecosystem dynamics. J. Chem. Ecol . 36: 2– 21. Google Scholar CrossRef Search ADS PubMed  Lindroth, R. L., Wood, S. A., and B. J. Kopper. 2002. Response of quaking aspen genotypes to enriched CO2: foliar chemistry and tussock moth performance. Agricultural and Forest Entomology 4: 315–323. Mattson, W. J. 1980. Herbivory in relation to plant nitrogen content. Annu. Rev. Ecol. Evol. Syst  11: 119– 161. Google Scholar CrossRef Search ADS   Murray, T. J., D. S. Ellsworth, D. T. Tissue, and M. Riegler. 2013. Interactive direct and plant-mediated effects of elevated atmospheric [CO2] and temperature on a eucalypt-feeding insect herbivore. Glob. Chang. Biol . 19: 1407– 1416. Google Scholar CrossRef Search ADS PubMed  Nicolas, G. A., and D. Sillans. 1989. Immediate and latent effects of carbon dioxide on insects. Ann. Rev. Entomol . 34: 97– 116. Google Scholar CrossRef Search ADS   Norby, R. J., E. H. DeLucia, B. Gielen, C. Calfapietra, C. P. Giardina, J. S. King, J. Ledford, H. R. McCarthy, D. J. P. Moore, R. Ceulmans,et al.   2005. Forest response to elevated CO2 is conserved across a broad range of productivity. Proc. Natl. Acad. Sci. USA . 102: 18052– 18056. Google Scholar CrossRef Search ADS   O’Neill, B. F., A. R. Zangerl, O. Dermody, D. D. Bilgin, C. L. Casteel, J. A. Zavala, E. H. DeLucia, and M. R. Berenbaum. 2010. Impact of elevated levels of atmospheric CO2 and herbivory on flavonoids of soybean (Glycine max Linnaeus). J. Chem. Ecol . 36: 35– 45. Google Scholar CrossRef Search ADS PubMed  Pennings, S. C., M. T. Nadeau, and V. J. Paul. 1993. Selectivity and growth of the generalist herbivore dolabella auricularia feeding upon complementary resources. Ecology  74: 879– 890. Google Scholar CrossRef Search ADS   Poorter, H. 1993. Interspecific variation in the growth response of plants to an elevated ambient CO2 concentration. Vegetatio  104: 77– 97. Google Scholar CrossRef Search ADS   Rogers, H. H., and R. C. Dahlman. 1993. Crop responses to CO2, enrichment. Vegetatio  104–105: 117– 131. Google Scholar CrossRef Search ADS   Rogers, H. H., G. B. Runion, and S. V. Krupa. 1994. Plant responses to atmospheric CO2 enrichment with emphasis on roots and the rhizosphere. Environ. Pollut . 83: 155– 189. Google Scholar CrossRef Search ADS PubMed  Roth, S. K., and R. L. Lindroth. 1995. Elevated atmospheric CO2: effects on phytochemistry, insect performance and insect-parasitoid interactions. Glob. Chang. Biol . 1: 173– 182. Google Scholar CrossRef Search ADS   Rowan, G. B., H. R. Boerma, J. N. All, and J. Todd. 1991. Soybean cultivar resistance to defoliating insects. Crop Sci . 31: 678– 682. Schade, J. D., M. Kyle, S. E. Hobbie, W. F. Fagan, and J. J. Elser. 2003. Stoichiometric tracking of soil nutrients by a desert insect herbivore. Ecol. Lett . 6: 96– 101. Google Scholar CrossRef Search ADS   Srinivasa, R. M., D. Manimanjari, M. Vanaja, C.A. Rama Rao, K. Srinivas, V. U. Rao, and B. Venkateswarlu. 2012. Impact of elevated CO2 on tobacco caterpillar, Spodoptera litura on peanut, Arachis hypogea. J. Insect Sci . 12: 1– 10. Stocker, T., Qin, D., Plattner, G., Tignor, M., Allen, S., and Boschung, J., et al. 2013. IPCC, 2013: climate change 2013: the physical science basis. contribution of working group i to the fifth assessment report of the intergovernmental panel on climate change. Comput. Geom. 18: 95–123. Su, Y., Y. F. Zhang, W. Y. Mou, G. N. Xing, and F. J. Chen. 2016. Responses of morphological trait and yield of soybean to elevated atmospheric CO2 concentration and temperature. Acta Ecologica Sinica . 36: 2597– 2606. Tester, C. F. 1977. Constituents of soybean cultivars differing in insect resistance. Phytochemistry  16: 1899– 1901. Google Scholar CrossRef Search ADS   Vanni, M. J., A. S. Flecker, M. James, J. Hood, and J. L. Headworth. 2002. Stoichiometry of nutrient recycling by vertebrates in a tropical stream: linking species identity and ecosystem processes. Ecol. Lett . 5: 285– 293. Google Scholar CrossRef Search ADS   Watson, R. T., M. C. Zinyowera, and R. H. Moss. 1996. Climate change 1995: impacts, adaptations and mitigation of climate change: scientific-technical analysis . Cambridge University Press, Cambridge, United Kingdom. Williams, R. S., D. E. Lincoln, and R. J. Norby. 1998. Leaf age effects of elevated CO2-grown white oak leaves on spring-feeding lepidopterans. Glob. Chang. Biol . 4: 235– 246. Google Scholar CrossRef Search ADS   Wu, Q. J., J. J. Wu, Y. C. Wu, H. Wang, J. Y. Gai, and D. Y. Yu. 2006. Evaluation of resistance of soybean germplasm to cotton worm (Spodopteral litura Fabricius). Soybean Sci . 25: 410– 413. Xing, G., K. Liu, and J. Gai. 2017. A high-throughput phenotyping procedure for evaluation of antixenosis against common cutworm at early seedling stage in soybean. Plant Methods . 13: 66. Google Scholar CrossRef Search ADS PubMed  Zavala, J. A., C. L. Casteel, P. D. Nabity, M. R. Berenbaum, and E. H. DeLucia. 2009. Role of cysteine proteinase inhibitors in preference of Japanese beetles (Popillia japonica) for soybean (Glycine max) leaves of different ages and grown under elevated CO2. Oecologia  161: 35– 41. Google Scholar CrossRef Search ADS PubMed  Zavala, J. A., P. D. Nabity, and E. H. DeLucia. 2013. An emerging understanding of mechanisms governing insect herbivory under elevated CO2. Annu. Rev. Entomol . 58: 79– 97. Google Scholar CrossRef Search ADS PubMed  Zhang, Y. F., Wan G. J., Liu B., Zhang X. G., Xing G. N., and F. J. Chen. 2018. Elevated CO2 and temperature alter development and food utilization of Spodoptera litura fed on resistant soybean. J. Appl. Entomol. 142: 250–262. Zhu, S. Y., and D. L. Hong. 2008. Comparison between two hybrid cultivars of indica rice (Oryza sativa L.) in seed vigor and biochemical traits after aging. Chin. J. Eco Agriculture  16: 396– 400. Google Scholar CrossRef Search ADS   Zhu, J. H., F. P. Zhang, and H. G. Ren. 2005. Development and nutrition of prodenia litura on four food plants. Entomol. Knowledg . 42: 643– 646. Ziska, L. H., O. Namuco, T. Moya, and J. Quilang. 1997. Growth and yield responses of field-grown tropical rice to increasing carbon dioxide and air temperature. Agron. J . 89: 45– 53. Google Scholar CrossRef Search ADS   Zvereva, E. L., and M. V. Kozlov. 2006. Consequences of simultaneous elevation of carbon dioxide and temperature for plant-herbivore interactions: a meta-analysis. Glob. Chang. Biol . 12: 27– 41. Google Scholar CrossRef Search ADS   © The Author(s) 2018. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Environmental Entomology Oxford University Press

Effects of Elevated CO2 on Plant Chemistry, Growth, Yield of Resistant Soybean, and Feeding of a Target Lepidoptera Pest, Spodoptera litura (Lepidoptera: Noctuidae)

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Entomological Society of America
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© The Author(s) 2018. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
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0046-225X
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1938-2936
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10.1093/ee/nvy060
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Abstract

Abstract Atmospheric CO2 level arising is an indisputable fact in the future climate change, as predicted, it could influence crops and their herbivorous insect pests. The growth and development, reproduction, and consumption of Spodoptera litura (F.) (Lepidoptera: Noctuidae) fed on resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean grown under elevated (732.1 ± 9.99 μl/liter) and ambient (373.6 ± 9.21 μl/liter) CO2 were examined in open-top chambers from 2013 to 2015. Elevated CO2 promoted the above- and belowground-biomass accumulation and increased the root/shoot ratio of two soybean cultivars, and increased the seeds’ yield for Lamar. Moreover, elevated CO2 significantly reduced the larval and pupal weight, prolonged the larval and pupal life span, and increased the feeding amount and excretion amount of two soybean cultivars. Significantly lower foliar nitrogen content and higher foliar sugar content and C/N ratio were observed in the sampled foliage of resistant and susceptible soybean cultivars grown under elevated CO2, which brought negative effects on the growth of S. litura, with the increment of foliar sugar content and C/N ratio were greater in the resistant soybean in contrast to the susceptible soybean. Furthermore, the increment of larval consumption was less than 50%, and the larval life span was prolonged more obvious of the larvae fed on resistant soybean compared with susceptible soybean under elevated CO2. It speculated that the future climatic change of atmospheric CO2 level arising would likely cause the increase of the soybean yield and the intake of S. litura, but the resistant soybean would improve the resistance of the target Lepidoptera pest, S. litura. elevated carbon dioxide, resistant soybean, plant chemistry, growth and yield, development and consumption Human influence on the climate system is clear and recent anthropogenic emissions of greenhouse gases are the highest in history (IPCC 2014). Atmospheric carbon dioxide (CO2) concentration has increased by more than 44%, from 280 ppm in the pre-industrial period (IPCC 2014) to 404 ppm in October of 2017 (www.esrl.noaa.gov/gmd/ccgg/trends/) and it is projected to increase to 550 ppm by 2050 and may surpass to 700 ppm by 2100 (Stocker et al. 2013). The atmospheric CO2 level arising has received considerable attention because it has marked effects on plant phytochemistry, growth and yield, and feeding behavior of phytophagous insect pests, which can in turn influence agro-ecosystem processes and crop productivity (Norby et al. 2005, Zvereva and Kozlov 2006, Lindroth 2010, O’Neill et al. 2010, Ainsworth et al. 2012a). The atmospheric CO2 concentration arising is likely to affect biota indirectly via climate change, and directly by producing changes not only in plant growth and allocation, but also in plant tissue chemical composition (Srinivasa et al. 2012). Legumes, more responsive to elevated CO2 than other plants, will have a competitive advantage when growing under elevated CO2 (Ainsworth and Long 2005). Elevated CO2 is generally expected to enhance the photosynthesis of crop species which utilize the C3 photosynthetic pathway (Drake et al. 1997, Ziska et al. 1997, Kim et al. 2003), leading to increases in the growth, yields and C/N ratios of agricultural crops (Bazzaz 1990, Horie et al. 2000, Kimball et al. 2002). The interactions between insect pests and their host plants change in response to the effects of CO2 on plant nutritional quality (Chen et al. 2005, Ainsworth et al. 2007). Due to the accumulation of nonstructural carbohydrates of plants grown under elevated CO2 (Williams et al. 1998), it declined the nutritional quality of plant leaves (Coley 1998). Many insects, especially some Lepidoptera insects will confront less nutritious host plants under elevated CO2, which will prolong the larval developmental duration and increase their intake (e.g. Helicoverpa armigera, Chen et al. 2005, Orgyia leucostigma, Lindroth et al. 2002). Soybean (Glycine max [L.] Merr.) is one of the important crops with high contents of edible protein and oil (Ainsworth et al. 2012b). Elevated CO2 caused a significant increase in total biomass and seed yield of the high photosynthetic efficiency soybean cultivars (Su et al. 2016). Spodoptera litura (F.) (Lepidoptera: Noctuidae) is a major leaf-chewing herbivorous insect of soybean, and it can cause heavily yield losses (Armes et al. 1997). In fact, the applying resistant soybean accessions would contribute to the integrated pest management in a sustainable and environment-friendly manner (Chen et al. 2012). Among the plant introductions from USDA Soybean Germplasm Collection, PI229358 was used in resistant breeding against insect pests because of multiple resistances to several species of herbivorous insects, especially some leaf-chewing insects (Lambert and Kilen 1984, Rowan et al. 1991). The soybean cultivar Lamar (PI533604) was selected and bred through cross-breeding with its resistant parental line PI229358 in Mississippi Agriculture and Forestry Experiment station (Hartwig et al. 1990). Lamar is considered as a highly resistant cultivar of soybean against S. litura and JLNMH as highly susceptible soybean cultivar for S. litura (Wu et al. 2006, Xing et al. 2017). Even though some studies have reported the effects of elevated CO2 on soybean and the herbivorous insect (Aldea et al. 2005, Hamilton et al. 2005, Zavala et al. 2009, Casteel et al. 2012, Murray et al. 2013). However, studies about the use of plants that differ in their resistance to a chewing herbivore are novel. We hypothesized that 1) the interaction between the chemical components in plants and the growth, development, and fecundity of chewing herbivores might be various in different resistant cultivars of soybean under elevated CO2, and 2) elevated CO2 might be more beneficial to the growth, yield, and resistance performance against insects in resistant soybeans than that of to susceptible soybeans. In this study, we used two soybean cultivars (i.e., the resistant cv. Lamar and the susceptible cv. JLNMH) to evaluate the impacts of elevated CO2 and resistant soybean on plant chemistry, growth, and yield of soybean and the relationship between plant chemistry change of resistant soybean and the growth, development, reproduction, and consumption of S. litura under elevated CO2. Materials and Methods Open-Top Chambers Six open-top chambers (OTCs, Granted Patent: ZL201120042889.1; 2.5 m in height × 3.2 m in diameter) (Chen et al. 2011) were constructed at the Innovation Research Platforms for Climate Change, Biodiversity and Pest Management (CCBPM; http://www.ccbpm.org) in Ningjin County, Shandong Province of China (37°38′ 30.7′′ N, 116°51′ 11.0′′ E). Two levels of atmospheric CO2 concentration were applied continuously, i.e., ambient level (2013: 368.5 ± 18.3 μl/liter, 2014: 384.2 ± 14.8 μl/liter, 2015: 368.0 ± 14.8 μl/liter; mean: 373.6 ± 9.21 μl/liter) and elevated level (2013: 723.6 ± 20.3 μl/liter, 2014: 743.1 ± 19.2 μl/liter, 2015: 729.6 ± 23.5 μl/liter; mean: 732.1 ± 9.99 μl/liter), representing the predicted level in about 100 yr (Watson et al. 1996, Houghton et al. 2001), from 14 June to 13 October in 2013, 2014, and 2015, respectively. Three OTCs were used for each CO2 treatment, and the CO2 concentration in each OTC was monitored continuously and adjusted with an infrared CO2 analyzer (Ventostat 8102; Telaire Company, Goleta, CA) on every day to ensure relatively stable CO2 concentrations. The OTCs with elevated CO2 were injected with canned CO2 gas with 95% purity and controlled via automated CO2 concentration monitor (Chen and Ge 2004). Air temperature and relative humidity were monitored continuously by using an automatic temperature analysis system (U23-001, HOBO Pro V2 Temp/RH Data Logger; MicroDAQ.com, Ltd, Contoocook, NH, USA) in each OTC throughout the field experiment. Actual mean temperature and relative humidity from 2013 to 2015 were shown in Table 1. Table 1. Actual mean temperature and relative humidity in the OTCs of ambient CO2 (i.e., aCO2) and elevated CO2 (i.e., eCO2) from 14 June to 13 October in 2013, 2014, and 2015, respectively (Mean ± SD) Year  CO2 treatments  Actual temperature (°C, 24 h/d)  Actual relative humidity (%, 24 h/d)  2013  eCO2  26.93 ± 0.36a  45.12 ± 2.97a  aCO2  26.41 ± 0.12a  46.34 ± 2.80a  2014  eCO2  27.12 ± 0.49a  48.75 ± 4.65a  aCO2  26.74 ± 0.21a  49.53 ± 4.14a  2015  eCO2  26.64 ± 0.36a  47.76 ± 2.31a  aCO2  26.30 ± 0.29a  51.48 ± 3.26a  Year  CO2 treatments  Actual temperature (°C, 24 h/d)  Actual relative humidity (%, 24 h/d)  2013  eCO2  26.93 ± 0.36a  45.12 ± 2.97a  aCO2  26.41 ± 0.12a  46.34 ± 2.80a  2014  eCO2  27.12 ± 0.49a  48.75 ± 4.65a  aCO2  26.74 ± 0.21a  49.53 ± 4.14a  2015  eCO2  26.64 ± 0.36a  47.76 ± 2.31a  aCO2  26.30 ± 0.29a  51.48 ± 3.26a  The same lowercase letters indicate no significant difference between ambient and elevated CO2 in same year by the Duncan’s test at P > 0.05. View Large Table 1. Actual mean temperature and relative humidity in the OTCs of ambient CO2 (i.e., aCO2) and elevated CO2 (i.e., eCO2) from 14 June to 13 October in 2013, 2014, and 2015, respectively (Mean ± SD) Year  CO2 treatments  Actual temperature (°C, 24 h/d)  Actual relative humidity (%, 24 h/d)  2013  eCO2  26.93 ± 0.36a  45.12 ± 2.97a  aCO2  26.41 ± 0.12a  46.34 ± 2.80a  2014  eCO2  27.12 ± 0.49a  48.75 ± 4.65a  aCO2  26.74 ± 0.21a  49.53 ± 4.14a  2015  eCO2  26.64 ± 0.36a  47.76 ± 2.31a  aCO2  26.30 ± 0.29a  51.48 ± 3.26a  Year  CO2 treatments  Actual temperature (°C, 24 h/d)  Actual relative humidity (%, 24 h/d)  2013  eCO2  26.93 ± 0.36a  45.12 ± 2.97a  aCO2  26.41 ± 0.12a  46.34 ± 2.80a  2014  eCO2  27.12 ± 0.49a  48.75 ± 4.65a  aCO2  26.74 ± 0.21a  49.53 ± 4.14a  2015  eCO2  26.64 ± 0.36a  47.76 ± 2.31a  aCO2  26.30 ± 0.29a  51.48 ± 3.26a  The same lowercase letters indicate no significant difference between ambient and elevated CO2 in same year by the Duncan’s test at P > 0.05. View Large Soybean Cultivars and Treatment Setup The resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean cultivars to S. litura were selected in this study. These two soybean cultivars were both supplied by the National Center for Soybean Improvement, Nanjing Agricultural University. Four treatments of both CO2 levels and two soybean cultivars were set up, including: 1) resistant soybean grown in ambient CO2 (aLamar), 2) resistant soybean grown in elevated CO2 (eLamar), 3) susceptible soybean grown in ambient CO2 (aJLNMH), and 4) susceptible soybean grown in elevated CO2 (aJLNMH). From 2013 to 2015, the resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean cultivars were planted in plastic buckets (diameter × height = 30 cm × 45 cm) filled with 2: 1 (by volume) loam: organic cultivation substrate and randomly placed in chambers on 14 June in 2013, 2014, and 2015, respectively. Nine buckets for each soybean cultivar were placed randomly in each OTC, and 10 soybean seeds were sown in each bucket. When plants reached the V4 (fourth compound leaves) stage (Fehr et al. 1971), extra plants were thinned out and six plants remained in each bucket. No chemical fertilizers or insecticides were used during the experiment. To standardize soil moisture across treatments, each bucket was irrigated with 2 liters water once every 4 d during the whole experimental period. Soybean Growth Traits, Yield, and Foliar Sugar and N Contents During the R4 (full pods) stage of soybean plants (Fehr et al. 1971), one bucket was randomly selected from each treatment of aLamar, eLamar, aJLNMH, and eJLNMH, respectively. Three sampled plants were dried at 80°C for 72 h and measured the dry weight per plant (including aboveground and belowground weight), and nine leaves from other three sampled plants (three leaflets from each sampled plant at same leaf position) were fixated at 105°C for 30 min, then oven-dried at 80°C for 72 h and weighted the dry weight per leaf. Moreover, the sampled dry leaves were grounded into powder, and then analyzed the contents of foliar sugar (anthrone colorimetry) (Zhu and Hong 2008), nitrogen (Kjeldahl method) (EMBRAPA 2009) and the C/N ratio (sugar content/nitrogen content) (Deng et al. 2012). During the R6 (full seeds) stage of soybean plants (Fehr et al. 1971), in the same way, dry weight per plant, contents of foliar sugar, N, and C/N ratio, were calculated. At the R8 stage (i.e., full maturity; Fehr et al. 1971), the soybean plants of the four treatments of aLamar, eLamar, aJLNMH, and eJLNMH were harvested and nine soybean plants were randomly selected from each OTC to measure the seed weight per plant, respectively. Insect Stocks and Rearing Egg masses of S. litura were collected from the Henan Jiyuan Baiyun Industrial Co., Ltd, and reared in the growth chambers (Model: GXZ-500B; Accuracy: temp: ±1°C, humidity: ±1%; Manufacturer: Ningbo JIANGNAN Ltd., Ningbo, China) under the control environment (temp: 27 ± 1°C; photoperiod: 14:10 (L:D) h; relative humidity: 70 ± 10%) for incubation. Twenty neonate larvae as one replication were placed in a disinfected plastic box (150 mm in diameter and 100 mm in height). Three replications (60 larvae) were kept for each treatment of two CO2 levels and two soybean cultivars, i.e., total 240 larvae for the whole experiment. The bioassay was done at growth chamber and the larvae of S. litura were fed with different sources of soybean from OTCs. Neonate larvae were reared on detached leaves of two soybean cultivars grown in two CO2 levels in the respective OTCs. The feeding trial was conducted between the R4 (full pods) and R6 (full seeds) stages of soybean plants (Fehr et al. 1971). The detached leaves were collected daily and randomly taken from the two soybean cultivars grown in two CO2 levels (the same leaf position at each collection) and used for the rearing after cleaning and drying. Two leaves were extracted, one of them was weighed and dried at 80°C for 72 h and measured the dry weight using electronic balance (Model: AL104; Accuracy: ±0.1 mg; METTLER-TOLEDO, Switzerland) in order to compute the foliar ratio of dry weight divided by fresh weight (i.e., DW/FW). The other one was offered to the larvae after weighing, and 24 h later the rest of this leaf and fecal matter of S. litura were dried at 80°C for 72 h to measure their dry weight by using the foliar ratio of DW/FW. Moreover, the consumption of larvae was calculated by using the mean leaf weight consumed minus the fecal matter weight per larva. The same process was repeated each day until the larvae grown to the third instar, and then the large larvae were fed separately in marked glass Petri dish (diameter:height = 60:16 mm), considering the cannibalism of old/late instar larvae of S. litura (Deng et al. 2015). In the same way of feeding mentioned above, the leaf weight consumed and the fecal matter weight per larva were calculated based on the above same protocol. In this process, once the larvae die, the corresponding record was deleted. When the larvae halted eating, a part of larvae were dried at 80°C for 72 h and measured the dry weight, and another part of larvae were collected until pupation. Growth, Development, and Fecundity of S. litura During the entire experiment, the tested larvae of S. litura were reared with new detached soybean leaves from the four treatments of aLamar, eLamar, aJLNMH, and eJLNMH, and simultaneously removed the excrements of S. litura larvae every day; the ecdysis and development of larvae were observed and recorded three times every day (average interval 8 h). The total consumption and fecal matter per larva were calculated. The pupal weight of S. litura was recorded on the second day after pupation, and the adult eclosion was also observed. After eclosion, S. litura moths were allowed for mating in cages (35 cm in length × 35 cm in width × 40 cm in height), and the paired moths of one female and one male were put in a plastic cup (8 cm in diameter × 20 cm in height) with a net cover of degreased cotton yarn for oviposition, and these adults were fed with 10% honey solution. The cotton yarns were replaced every day and the eggs laid on each disc were counted and recorded daily. Data Analysis All data were analyzed by using the SAS v. 9.4. The Levene’s test was used to test the homoscedasticity of variances (P > 0.10), and the Shapiro-Wilk test was used to examine the normality of the experimental data (P > 0.05). Moreover, three-factor ANOVAs were used to identify the influence of CO2 levels (elevated CO2 vs. ambient CO2), soybean cultivars (the resistant cv. Lamar vs. the susceptible cv. JLNMH), sampling years (2013, 2014, 2015), and their bi- and tri-interactions on the biomass, yield and foliar chemistry of soybean, and on the growth, development and reproduction, feeding and excretion of S. litura. The measured indexes of soybean include the aboveground and belowground biomass, root/shoot ratio, foliar sugar and N contents, foliar C/N ratio, and seeds weight of soybean plants. The measured indexes of S. litura include feeding and excretion amount and net consumption per larva, larval and pupal life span, larval and pupal weight, and fecundity. Moreover, the Duncan’s test was used to analyze the significant difference in the measured indexes of soybean and S. litura between ambient and elevated CO2 for same soybean cultivar, and between the resistant and susceptible soybean cultivars under same CO2 level at P < 0.05, respectively. Furthermore, the Pearson’s correlation analysis was used to analyze the significant difference between the measured indexes of the foliar chemistry of soybean and the growth of S. litura in different of CO2 levels (elevated vs. ambient) and sampling years (2013, 2014 and 2015) at P < 0.05, 0.01 or 0.001. Results Effects of Soybean Cultivar and Elevated CO2 on the Growth, Foliar Chemistry, and Yield of Soybean CO2 levels and soybean cultivars significantly affected the aboveground biomass, foliar sugar and N contents, foliar C/N ratio both at R4 and R6 stages of soybean, and the seeds weight per plant (P < 0.01 or 0.001; Table 2); the belowground biomass was significantly affected by soybean cultivars both at R4 and R6 stages (P < 0.05 and 0.001; Table 2), and significantly affected by CO2 levels at R6 stage (P < 0.05; Table 2); the root/shoot ratio was just significantly affected by soybean cultivars at R4 stage (P < 0.05; Table 2). Moreover, there was a significant difference in the seeds weight per plant among sampling years (P < 0.001; Table 2). Table 2. Three-way ANOVA of CO2 levels (elevated vs. ambient), soybean cultivars (resistant vs. susceptible), sampling years (2013, 2014 and 2015) and their bi- and tri-interactions on the biomass, foliar chemistry at the R4 (full pods) and the R6 (full seeds) stages, and the yield at the R8 (full maturity) stage of soybean plants, and on the growth, development and reproduction, feeding and excretion of Spodoptera litura in 2013–2015 (F values) Measured indexes  CO2a  Cv.b  Year  CO2 × Cv.  CO2 × year  Year × Cv.  Year × CO2 × Cv.  Soybean  R4  Aboveground biomass (dry weight; g/plant)  9.1†  36.7‡  0.4  0.2  0.1  0.3  0.9  Belowground biomass (dry weight; g/plant)  1.1  5.3*  1.5  0.1  0.2  0.3  0.0  Root/shoot ratio (%)  1.6  5.0*  1.0  1.2  0.2  0.9  0.1  Foliar sugar (%)  109.0‡  110.3‡  0.1  21.7‡  0.1  1.1  0.1  Foliar nitrogen (%)  20.3‡  123.8‡  0.3  0. 9  0.8  0.3  0.1  Foliar C/N ratio  54.9‡  127.5‡  0.1  17.3‡  0.4  0.1  0.2  R6  Aboveground biomass (dry weight; g/plant)  23.4‡  95.3‡  0.8  0.6  1.1  0.2  0.4  Belowground biomass (dry weight; g/plant)  5.7*  28.9‡  0.4  1.3  0.4  0.4  0.0  Root/shoot ratio (%)  0.8  1.4  0.1  0.2  0.1  0.1  0.0  Foliar sugar (%)  50.1‡  81.4‡  0.3  10.7†  0.1  0.1  0.2  Foliar nitrogen (%)  36.9‡  400.5‡  3.4  0.0  3.1  1.2  0.5  Foliar C/N ratio  132.7‡  547.0‡  0.3  42.6‡  3.0  0.1  0.9  R8  Seeds weight (dry weight; g/plant)  45.1‡  1399.3‡  10.0‡  17.5‡  1.7  4.9*  0.2  S. litura  Larval life span (day)  50.8‡  114.4‡  2.6  10.0†  0.8  0.8  0.3  Pupal life span (day)  16.5‡  126.4‡  0.3  0.9  0.6  0.5  0.5  Larval weight (g)  172. 0‡  779.3‡  0.4  28.2‡  5.0*  0.4  0.3  Pupal weight (g)  20.4‡  178.7‡  1.7  1.5  0.3  1.1  0.8  Fecundity (eggs laid per female)  49.6‡  790.7‡  0.3  0.0  0.1  3.8*  0.8  Feeding amount (dry weight; g/larva)  753.8‡  3850.5‡  2.0  323.5‡  1.5  0.4  1.2  Excretion amount (dry weight; g/larva)  577.1‡  3448.0‡  1.3  67.0‡  0.2  0.3  0.4  Net consumption (dry weight; g/larva)  840.0‡  3825.5‡  4.9*  636.2‡  5.9†  2.5  5.3†  Measured indexes  CO2a  Cv.b  Year  CO2 × Cv.  CO2 × year  Year × Cv.  Year × CO2 × Cv.  Soybean  R4  Aboveground biomass (dry weight; g/plant)  9.1†  36.7‡  0.4  0.2  0.1  0.3  0.9  Belowground biomass (dry weight; g/plant)  1.1  5.3*  1.5  0.1  0.2  0.3  0.0  Root/shoot ratio (%)  1.6  5.0*  1.0  1.2  0.2  0.9  0.1  Foliar sugar (%)  109.0‡  110.3‡  0.1  21.7‡  0.1  1.1  0.1  Foliar nitrogen (%)  20.3‡  123.8‡  0.3  0. 9  0.8  0.3  0.1  Foliar C/N ratio  54.9‡  127.5‡  0.1  17.3‡  0.4  0.1  0.2  R6  Aboveground biomass (dry weight; g/plant)  23.4‡  95.3‡  0.8  0.6  1.1  0.2  0.4  Belowground biomass (dry weight; g/plant)  5.7*  28.9‡  0.4  1.3  0.4  0.4  0.0  Root/shoot ratio (%)  0.8  1.4  0.1  0.2  0.1  0.1  0.0  Foliar sugar (%)  50.1‡  81.4‡  0.3  10.7†  0.1  0.1  0.2  Foliar nitrogen (%)  36.9‡  400.5‡  3.4  0.0  3.1  1.2  0.5  Foliar C/N ratio  132.7‡  547.0‡  0.3  42.6‡  3.0  0.1  0.9  R8  Seeds weight (dry weight; g/plant)  45.1‡  1399.3‡  10.0‡  17.5‡  1.7  4.9*  0.2  S. litura  Larval life span (day)  50.8‡  114.4‡  2.6  10.0†  0.8  0.8  0.3  Pupal life span (day)  16.5‡  126.4‡  0.3  0.9  0.6  0.5  0.5  Larval weight (g)  172. 0‡  779.3‡  0.4  28.2‡  5.0*  0.4  0.3  Pupal weight (g)  20.4‡  178.7‡  1.7  1.5  0.3  1.1  0.8  Fecundity (eggs laid per female)  49.6‡  790.7‡  0.3  0.0  0.1  3.8*  0.8  Feeding amount (dry weight; g/larva)  753.8‡  3850.5‡  2.0  323.5‡  1.5  0.4  1.2  Excretion amount (dry weight; g/larva)  577.1‡  3448.0‡  1.3  67.0‡  0.2  0.3  0.4  Net consumption (dry weight; g/larva)  840.0‡  3825.5‡  4.9*  636.2‡  5.9†  2.5  5.3†  aCO2: CO2 levels (elevated vs. ambient). bCv.: Soybean cultivars (resistant vs. susceptible). *P < 0.05, †P < 0.01, ‡P < 0.001. View Large Table 2. Three-way ANOVA of CO2 levels (elevated vs. ambient), soybean cultivars (resistant vs. susceptible), sampling years (2013, 2014 and 2015) and their bi- and tri-interactions on the biomass, foliar chemistry at the R4 (full pods) and the R6 (full seeds) stages, and the yield at the R8 (full maturity) stage of soybean plants, and on the growth, development and reproduction, feeding and excretion of Spodoptera litura in 2013–2015 (F values) Measured indexes  CO2a  Cv.b  Year  CO2 × Cv.  CO2 × year  Year × Cv.  Year × CO2 × Cv.  Soybean  R4  Aboveground biomass (dry weight; g/plant)  9.1†  36.7‡  0.4  0.2  0.1  0.3  0.9  Belowground biomass (dry weight; g/plant)  1.1  5.3*  1.5  0.1  0.2  0.3  0.0  Root/shoot ratio (%)  1.6  5.0*  1.0  1.2  0.2  0.9  0.1  Foliar sugar (%)  109.0‡  110.3‡  0.1  21.7‡  0.1  1.1  0.1  Foliar nitrogen (%)  20.3‡  123.8‡  0.3  0. 9  0.8  0.3  0.1  Foliar C/N ratio  54.9‡  127.5‡  0.1  17.3‡  0.4  0.1  0.2  R6  Aboveground biomass (dry weight; g/plant)  23.4‡  95.3‡  0.8  0.6  1.1  0.2  0.4  Belowground biomass (dry weight; g/plant)  5.7*  28.9‡  0.4  1.3  0.4  0.4  0.0  Root/shoot ratio (%)  0.8  1.4  0.1  0.2  0.1  0.1  0.0  Foliar sugar (%)  50.1‡  81.4‡  0.3  10.7†  0.1  0.1  0.2  Foliar nitrogen (%)  36.9‡  400.5‡  3.4  0.0  3.1  1.2  0.5  Foliar C/N ratio  132.7‡  547.0‡  0.3  42.6‡  3.0  0.1  0.9  R8  Seeds weight (dry weight; g/plant)  45.1‡  1399.3‡  10.0‡  17.5‡  1.7  4.9*  0.2  S. litura  Larval life span (day)  50.8‡  114.4‡  2.6  10.0†  0.8  0.8  0.3  Pupal life span (day)  16.5‡  126.4‡  0.3  0.9  0.6  0.5  0.5  Larval weight (g)  172. 0‡  779.3‡  0.4  28.2‡  5.0*  0.4  0.3  Pupal weight (g)  20.4‡  178.7‡  1.7  1.5  0.3  1.1  0.8  Fecundity (eggs laid per female)  49.6‡  790.7‡  0.3  0.0  0.1  3.8*  0.8  Feeding amount (dry weight; g/larva)  753.8‡  3850.5‡  2.0  323.5‡  1.5  0.4  1.2  Excretion amount (dry weight; g/larva)  577.1‡  3448.0‡  1.3  67.0‡  0.2  0.3  0.4  Net consumption (dry weight; g/larva)  840.0‡  3825.5‡  4.9*  636.2‡  5.9†  2.5  5.3†  Measured indexes  CO2a  Cv.b  Year  CO2 × Cv.  CO2 × year  Year × Cv.  Year × CO2 × Cv.  Soybean  R4  Aboveground biomass (dry weight; g/plant)  9.1†  36.7‡  0.4  0.2  0.1  0.3  0.9  Belowground biomass (dry weight; g/plant)  1.1  5.3*  1.5  0.1  0.2  0.3  0.0  Root/shoot ratio (%)  1.6  5.0*  1.0  1.2  0.2  0.9  0.1  Foliar sugar (%)  109.0‡  110.3‡  0.1  21.7‡  0.1  1.1  0.1  Foliar nitrogen (%)  20.3‡  123.8‡  0.3  0. 9  0.8  0.3  0.1  Foliar C/N ratio  54.9‡  127.5‡  0.1  17.3‡  0.4  0.1  0.2  R6  Aboveground biomass (dry weight; g/plant)  23.4‡  95.3‡  0.8  0.6  1.1  0.2  0.4  Belowground biomass (dry weight; g/plant)  5.7*  28.9‡  0.4  1.3  0.4  0.4  0.0  Root/shoot ratio (%)  0.8  1.4  0.1  0.2  0.1  0.1  0.0  Foliar sugar (%)  50.1‡  81.4‡  0.3  10.7†  0.1  0.1  0.2  Foliar nitrogen (%)  36.9‡  400.5‡  3.4  0.0  3.1  1.2  0.5  Foliar C/N ratio  132.7‡  547.0‡  0.3  42.6‡  3.0  0.1  0.9  R8  Seeds weight (dry weight; g/plant)  45.1‡  1399.3‡  10.0‡  17.5‡  1.7  4.9*  0.2  S. litura  Larval life span (day)  50.8‡  114.4‡  2.6  10.0†  0.8  0.8  0.3  Pupal life span (day)  16.5‡  126.4‡  0.3  0.9  0.6  0.5  0.5  Larval weight (g)  172. 0‡  779.3‡  0.4  28.2‡  5.0*  0.4  0.3  Pupal weight (g)  20.4‡  178.7‡  1.7  1.5  0.3  1.1  0.8  Fecundity (eggs laid per female)  49.6‡  790.7‡  0.3  0.0  0.1  3.8*  0.8  Feeding amount (dry weight; g/larva)  753.8‡  3850.5‡  2.0  323.5‡  1.5  0.4  1.2  Excretion amount (dry weight; g/larva)  577.1‡  3448.0‡  1.3  67.0‡  0.2  0.3  0.4  Net consumption (dry weight; g/larva)  840.0‡  3825.5‡  4.9*  636.2‡  5.9†  2.5  5.3†  aCO2: CO2 levels (elevated vs. ambient). bCv.: Soybean cultivars (resistant vs. susceptible). *P < 0.05, †P < 0.01, ‡P < 0.001. View Large Compared with ambient CO2, elevated CO2 significantly increased the aboveground biomass, foliar sugar content and C/N ratio of the resistant and susceptible soybean at the R4 (Lamar: +20.28, +27.08, and +51.09%; JLNMH: +10.88, +11.72, and +22.58%) and R6 (Lamar: +17.47, +21.43, and +44.44%; JLNMH: +17.54, +9.30, and +21.92%) stages respectively (P < 0.05; Table 3), and significantly increased the belowground biomass of the susceptible soybean at the R6 stage (+13.96%; P < 0.05; Table 3). Moreover, elevated CO2 reduced the root/shoot ratio at the R4 and R6 stages of resistant and susceptible soybean respectively, but not significantly compared with ambient CO2 (P > 0.05; Table 3). Furthermore, elevated CO2 significantly decreased the foliar nitrogen content of resistant and susceptible cultivars of soybean at the R4 (Lamar: −16.20%; JLNMH: −8.15%) and R6 (Lamar: −15.81%; JLNMH: −10.14%) stages respectively (P < 0.05; Table 3). Finally, elevated CO2 significantly increased the seeds weight per plant of resistant soybean in 2013, 2014, and 2015 (+16.22, +26.01, and +15.87%), and of susceptible soybean just in 2014 (+21.26%) (P < 0.05; Fig. 1). Table 3. The growth and foliar chemistry of resistant (cv. Lamar) and susceptible (cv. JLNMH) cultivars of soybean during the R4 (i.e., full pods) and R6 (i.e., full seeds) stages grown under ambient and elevated CO2 from 2013 to 2015 (Mean ± SD) Stage  Treatment  Aboveground biomass (g/plant)  Belowground biomass (g/plant)  Root/shoot ratio (%)  Foliar sugar (%)  Foliar nitrogen (%)  C/N ratio  R4  eLamar  16.49 ± 1.49aB  3.29 ± 0.78  20.14 ± 5.34  4.13 ± 0.17aA  3.00 ± 0.34bB  1.39 ± 0.17aA  aLamar  13.71 ± 2.27bB  3.13 ± 0.63  23.46 ± 4.45A  3.25 ± 0.17bA  3.58 ± 0.39aB  0.92 ± 0.12bA  eJLNMH  20.99 ± 3.25aA  3.86 ± 0.45  18.59 ± 2.46  3.24 ± 0.13aB  4.28 ± 0.18bA  0.76 ± 0.04aB  aJLNMH  18.93 ± 1.41bA  3.56 ± 0.52  18.83 ± 2.65B  2.90 ± 0.16bB  4.66 ± 0.21aA  0.62 ± 0.05bB  R6  eLamar  25.49 ± 1.97aB  4.13 ± 0.92B  16.37 ± 4.17  3.57 ± 0.19aA  1.97 ± 0.17bB  1.82 ± 0.14aA  aLamar  21.70 ± 2.64bB  3.85 ± 0.59B  17.84 ± 2.49  2.94 ± 0.15bA  2.34 ± 0.16aB  1.25 ± 0.08bA  eJLNMH  35.39 ± 3.15aA  5.58 ± 0.35aA  15.60 ± 2.32  2.82 ± 0.13aB  3.19 ± 0.19bA  0.89 ± 0.06aB  aJLNMH  30.11 ± 2.79bA  4.80 ± 0.40bA  16.06 ± 1.98  2.58 ± 0.19bB  3.55 ± 0.30aA  0.73 ± 0.06bB  Stage  Treatment  Aboveground biomass (g/plant)  Belowground biomass (g/plant)  Root/shoot ratio (%)  Foliar sugar (%)  Foliar nitrogen (%)  C/N ratio  R4  eLamar  16.49 ± 1.49aB  3.29 ± 0.78  20.14 ± 5.34  4.13 ± 0.17aA  3.00 ± 0.34bB  1.39 ± 0.17aA  aLamar  13.71 ± 2.27bB  3.13 ± 0.63  23.46 ± 4.45A  3.25 ± 0.17bA  3.58 ± 0.39aB  0.92 ± 0.12bA  eJLNMH  20.99 ± 3.25aA  3.86 ± 0.45  18.59 ± 2.46  3.24 ± 0.13aB  4.28 ± 0.18bA  0.76 ± 0.04aB  aJLNMH  18.93 ± 1.41bA  3.56 ± 0.52  18.83 ± 2.65B  2.90 ± 0.16bB  4.66 ± 0.21aA  0.62 ± 0.05bB  R6  eLamar  25.49 ± 1.97aB  4.13 ± 0.92B  16.37 ± 4.17  3.57 ± 0.19aA  1.97 ± 0.17bB  1.82 ± 0.14aA  aLamar  21.70 ± 2.64bB  3.85 ± 0.59B  17.84 ± 2.49  2.94 ± 0.15bA  2.34 ± 0.16aB  1.25 ± 0.08bA  eJLNMH  35.39 ± 3.15aA  5.58 ± 0.35aA  15.60 ± 2.32  2.82 ± 0.13aB  3.19 ± 0.19bA  0.89 ± 0.06aB  aJLNMH  30.11 ± 2.79bA  4.80 ± 0.40bA  16.06 ± 1.98  2.58 ± 0.19bB  3.55 ± 0.30aA  0.73 ± 0.06bB  aLamar and eLamar–the soybean resistant cultivar (cv. Lamar) grown under ambient and elevated CO2, respectively; aJLNMH and eJLNMH–the soybean susceptible cultivar (cv. JLNMH) grown under ambient and elevated CO2, respectively. Different lowercase and uppercase letters indicates significant difference between ambient CO2 and elevated CO2 for same soybean cultivar, and between resistant and susceptible soybean cultivars grown under same CO2 level by Duncan’s test at P < 0.05. The same as in the Table 4. View Large Table 3. The growth and foliar chemistry of resistant (cv. Lamar) and susceptible (cv. JLNMH) cultivars of soybean during the R4 (i.e., full pods) and R6 (i.e., full seeds) stages grown under ambient and elevated CO2 from 2013 to 2015 (Mean ± SD) Stage  Treatment  Aboveground biomass (g/plant)  Belowground biomass (g/plant)  Root/shoot ratio (%)  Foliar sugar (%)  Foliar nitrogen (%)  C/N ratio  R4  eLamar  16.49 ± 1.49aB  3.29 ± 0.78  20.14 ± 5.34  4.13 ± 0.17aA  3.00 ± 0.34bB  1.39 ± 0.17aA  aLamar  13.71 ± 2.27bB  3.13 ± 0.63  23.46 ± 4.45A  3.25 ± 0.17bA  3.58 ± 0.39aB  0.92 ± 0.12bA  eJLNMH  20.99 ± 3.25aA  3.86 ± 0.45  18.59 ± 2.46  3.24 ± 0.13aB  4.28 ± 0.18bA  0.76 ± 0.04aB  aJLNMH  18.93 ± 1.41bA  3.56 ± 0.52  18.83 ± 2.65B  2.90 ± 0.16bB  4.66 ± 0.21aA  0.62 ± 0.05bB  R6  eLamar  25.49 ± 1.97aB  4.13 ± 0.92B  16.37 ± 4.17  3.57 ± 0.19aA  1.97 ± 0.17bB  1.82 ± 0.14aA  aLamar  21.70 ± 2.64bB  3.85 ± 0.59B  17.84 ± 2.49  2.94 ± 0.15bA  2.34 ± 0.16aB  1.25 ± 0.08bA  eJLNMH  35.39 ± 3.15aA  5.58 ± 0.35aA  15.60 ± 2.32  2.82 ± 0.13aB  3.19 ± 0.19bA  0.89 ± 0.06aB  aJLNMH  30.11 ± 2.79bA  4.80 ± 0.40bA  16.06 ± 1.98  2.58 ± 0.19bB  3.55 ± 0.30aA  0.73 ± 0.06bB  Stage  Treatment  Aboveground biomass (g/plant)  Belowground biomass (g/plant)  Root/shoot ratio (%)  Foliar sugar (%)  Foliar nitrogen (%)  C/N ratio  R4  eLamar  16.49 ± 1.49aB  3.29 ± 0.78  20.14 ± 5.34  4.13 ± 0.17aA  3.00 ± 0.34bB  1.39 ± 0.17aA  aLamar  13.71 ± 2.27bB  3.13 ± 0.63  23.46 ± 4.45A  3.25 ± 0.17bA  3.58 ± 0.39aB  0.92 ± 0.12bA  eJLNMH  20.99 ± 3.25aA  3.86 ± 0.45  18.59 ± 2.46  3.24 ± 0.13aB  4.28 ± 0.18bA  0.76 ± 0.04aB  aJLNMH  18.93 ± 1.41bA  3.56 ± 0.52  18.83 ± 2.65B  2.90 ± 0.16bB  4.66 ± 0.21aA  0.62 ± 0.05bB  R6  eLamar  25.49 ± 1.97aB  4.13 ± 0.92B  16.37 ± 4.17  3.57 ± 0.19aA  1.97 ± 0.17bB  1.82 ± 0.14aA  aLamar  21.70 ± 2.64bB  3.85 ± 0.59B  17.84 ± 2.49  2.94 ± 0.15bA  2.34 ± 0.16aB  1.25 ± 0.08bA  eJLNMH  35.39 ± 3.15aA  5.58 ± 0.35aA  15.60 ± 2.32  2.82 ± 0.13aB  3.19 ± 0.19bA  0.89 ± 0.06aB  aJLNMH  30.11 ± 2.79bA  4.80 ± 0.40bA  16.06 ± 1.98  2.58 ± 0.19bB  3.55 ± 0.30aA  0.73 ± 0.06bB  aLamar and eLamar–the soybean resistant cultivar (cv. Lamar) grown under ambient and elevated CO2, respectively; aJLNMH and eJLNMH–the soybean susceptible cultivar (cv. JLNMH) grown under ambient and elevated CO2, respectively. Different lowercase and uppercase letters indicates significant difference between ambient CO2 and elevated CO2 for same soybean cultivar, and between resistant and susceptible soybean cultivars grown under same CO2 level by Duncan’s test at P < 0.05. The same as in the Table 4. View Large Fig. 1. View largeDownload slide The seeds weight of resistant (cv. Lamar) and susceptible (cv. JLNMH) cultivars of soybean grown under ambient and elevated CO2 in 2013, 2014, and 2015. Each value represents the average (±SD). Different lowercase and uppercase letters indicated significant differences between ambient CO2 (aCO2) and elevated CO2 (eCO2) for same soybean cultivar, and between resistant and susceptible cultivars of soybean grown under same CO2 level by the Duncan’s test as P < 0.05, respectively. Fig. 1. View largeDownload slide The seeds weight of resistant (cv. Lamar) and susceptible (cv. JLNMH) cultivars of soybean grown under ambient and elevated CO2 in 2013, 2014, and 2015. Each value represents the average (±SD). Different lowercase and uppercase letters indicated significant differences between ambient CO2 (aCO2) and elevated CO2 (eCO2) for same soybean cultivar, and between resistant and susceptible cultivars of soybean grown under same CO2 level by the Duncan’s test as P < 0.05, respectively. The aboveground biomass and foliar nitrogen content of the resistant soybean were significantly lower than that of the susceptible soybean during the R4 (Ambient CO2: −27.58 and −23.18%; Elevated CO2: −21.44 and −29.91%) and R6 (Ambient CO2: −27.93 and −34.08%; Elevated CO2: −27.97 and −38.24%) stages respectively (P < 0.05; Table 3), and the belowground biomass of the resistant soybean was significantly lower than that of the susceptible soybean at the R6 stage (Ambient CO2: −19.79%; Elevated CO2: −24.50%) (P < 0.05; Table 3). Moreover, the root/shoot ratio of resistant soybean was significantly higher than that of the susceptible soybean at the R4 stage under ambient CO2 (+22.84%; P < 0.05; Table 3). Furthermore, the foliar sugar content and C/N ratio of resistant soybean were significantly higher than that of susceptible soybean at the R4 (Ambient CO2: +12.07 and +48.39%; Elevated CO2: +27.47 and +82.89%) and R6 (Ambient CO2: +13.95 and +72.60%; Elevated CO2: +26.60 and +104.49%) stages respectively (P < 0.05; Table 3). Finally, the seeds weight per plant of the resistant soybean was significantly higher than that of the susceptible soybean in 2013 (Ambient CO2: +112.77%; Elevated CO2: +142.05%), 2014 (Ambient CO2: +178.84%; Elevated CO2: +189.77%) and 2015 (Ambient CO2: +141.43%; Elevated CO2: +150.84%) respectively (P < 0.05; Fig. 1). Effects of Soybean Cultivar and Elevated CO2 on the Growth and Development, Reproduction, and Consumption of S. litura CO2 levels and soybean cultivars significantly affected the larval and pupal life span, larval and pupal weight, fecundity, feeding and excretion amount per larva, and net consumption per larva of S. litura (P < 0.001; Table 2). Moreover, there was a significant difference in the net consumption per larva among sampling years (P < 0.05; Table 2). Compared with ambient CO2, elevated CO2 significantly prolonged the larval life span of S. litura fed on resistant soybean (2013: +8.26%; 2014: +8.41%; 2015: +7.21%) and susceptible soybean (2014: +4.95%) (P < 0.05; Table 3), and significantly prolonged the pupal life span of S. litura fed on resistant soybean in 2014 (+6.45%) and 2015 (+6.45%) (P < 0.05; Table 4). Moreover, elevated CO2 significantly reduced the larval weight and fecundity of S. litura fed on resistant and susceptible soybean in 2013 (Lamar: −14.29% and −19.61%; JLNMH: −19.23% and −9.07%), 2014 (Lamar: −7.41% and −15.85%; JLNMH: −11.84% and −7.79%), and 2015 (Lamar: −7.27% and −11.95%; JLNMH: −15.58% and −12.26%) respectively (P < 0.05; Table 4), and significantly reduced the pupal weight of S. litura fed on resistant soybean (2014: −17.24%; 2015: −10.71%) and susceptible soybean (2014: −12.82%) (P < 0.05; Table 4). Furthermore, elevated CO2 significantly increased the feeding and excretion amount per larva of S. litura fed on resistant and susceptible soybean in 2013 (Lamar: +16.19 and +43.33%; JLNMH: +40.11 and +38.36%), 2014 (Lamar: +16.04 and +43.33%; JLNMH: +45.16 and +38.89%), and 2015 (Lamar: +16.82 and +45.16%; JLNMH: +47.59 and +33.33%) respectively (P < 0.05; Table 4), and significantly increased the net consumption per larva of S. litura fed on susceptible soybean in three sampling years (2013: +41.23%; 2014: +49.12%; 2015: +57.14%; P < 0.05; Table 4). Table 4. Effects of elevated CO2 on the growth, development and reproduction, feeding and excretion of S. litura fed on resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean grown under ambient and elevated CO2 in 2013–2015 (Mean ± SD) Year  Treatment  Larval life span (day)  Pupal life span (day)  Larval weight (g)  Pupal weight (g)  Fecundity (eggs laid/female)  Feeding amount (dry weight; g/larva)  Excretion amount (dry weight; g/larva)  Net consumption (dry weight; g/larva)  2013  eLamar  23.6 ± 0.55aA  13.4 ± 0.55aA  0.48 ± 0.03bB  0.25 ± 0.04aB  306.6 ± 60.7bB  1.22 ± 0.03aB  0.43 ± 0.02aB  0.79 ± 0.02aB  aLamar  21.8 ± 0.45bA  13.0 ± 0.71aA  0.56 ± 0.02aB  0.29 ± 0.02aB  381.4 ± 23.6aB  1.05 ± 0.06bB  0.30 ± 0.03bB  0.75 ± 0.03aB  eJLNMH  21.4 ± 0.55aB  10.8 ± 1.30aB  0.63 ± 0.03bA  0.35 ± 0.04aA  593.6 ± 17.2bA  2.62 ± 0.11aA  1.01 ± 0.05aA  1.61 ± 0.06aA  aJLNMH  20.6 ± 0.55aB  10.0 ± 0.71aB  0.78 ± 0.04aA  0.35 ± 0.03aA  652.8 ± 29.8aA  1.87 ± 0.06bA  0.73 ± 0.03bA  1.14 ± 0.03bA  2014  eLamar  23.2 ± 0.84aA  13.2 ± 0.45aA  0.50 ± 0.01bB  0.24 ± 0.03bB  342.0 ± 20.2bB  1.23 ± 0.13aB  0.43 ± 0.05aB  0.80 ± 0.08aB  aLamar  21.4 ± 0.55bA  12.4 ± 0.55bA  0.54 ± 0.02aB  0.29 ± 0.02aB  406.4 ± 30.9aB  1.06 ± 0.03bB  0.30 ± 0.01bB  0.77 ± 0.01aB  eJLNMH  21.2 ± 0.45aB  11.0 ± 1.22aB  0.67 ± 0.01bA  0.34 ± 0.02bA  572.6 ± 27.1bA  2.70 ± 0.02aA  1.00 ± 0.01aA  1.70 ± 0.01aA  aJLNMH  20.2 ± 0.84bB  9.8 ± 0.45aB  0.76 ± 0.02aA  0.39 ± 0.01aA  621.0 ± 30.2aA  1.86 ± 0.03bA  0.72 ± 0.01bA  1.14 ± 0.02bA  2015  eLamar  23.8 ± 0.45aA  13.2 ± 0.45aA  0.51 ± 0.04bB  0.25 ± 0.01bB  336.0 ± 19.8bB  1.25 ± 0.08aB  0.45 ± 0.04aB  0.80 ± 0.03aB  aLamar  22.2 ± 0.84bA  12.4 ± 0.55bA  0.55 ± 0.02aB  0.28 ± 0.02aB  381.6 ± 30.1aB  1.07 ± 0.07bB  0.31 ± 0.04bB  0.76 ± 0.03aB  eJLNMH  21.0 ± 0.71aB  11.4 ± 1.14aB  0.65 ± 0.04bA  0.35 ± 0.02aA  557.0 ± 26.8bA  2.76 ± 0.09aA  1.00 ± 0.04aA  1.76 ± 0.05aA  aJLNMH  20.8 ± 0.84aB  10.2 ± 1.10aB  0.77 ± 0.02aA  0.37 ± 0.04aA  634.8 ± 57.9aA  1.87 ± 0.04bA  0.75 ± 0.02bA  1.12 ± 0.02bA  Year  Treatment  Larval life span (day)  Pupal life span (day)  Larval weight (g)  Pupal weight (g)  Fecundity (eggs laid/female)  Feeding amount (dry weight; g/larva)  Excretion amount (dry weight; g/larva)  Net consumption (dry weight; g/larva)  2013  eLamar  23.6 ± 0.55aA  13.4 ± 0.55aA  0.48 ± 0.03bB  0.25 ± 0.04aB  306.6 ± 60.7bB  1.22 ± 0.03aB  0.43 ± 0.02aB  0.79 ± 0.02aB  aLamar  21.8 ± 0.45bA  13.0 ± 0.71aA  0.56 ± 0.02aB  0.29 ± 0.02aB  381.4 ± 23.6aB  1.05 ± 0.06bB  0.30 ± 0.03bB  0.75 ± 0.03aB  eJLNMH  21.4 ± 0.55aB  10.8 ± 1.30aB  0.63 ± 0.03bA  0.35 ± 0.04aA  593.6 ± 17.2bA  2.62 ± 0.11aA  1.01 ± 0.05aA  1.61 ± 0.06aA  aJLNMH  20.6 ± 0.55aB  10.0 ± 0.71aB  0.78 ± 0.04aA  0.35 ± 0.03aA  652.8 ± 29.8aA  1.87 ± 0.06bA  0.73 ± 0.03bA  1.14 ± 0.03bA  2014  eLamar  23.2 ± 0.84aA  13.2 ± 0.45aA  0.50 ± 0.01bB  0.24 ± 0.03bB  342.0 ± 20.2bB  1.23 ± 0.13aB  0.43 ± 0.05aB  0.80 ± 0.08aB  aLamar  21.4 ± 0.55bA  12.4 ± 0.55bA  0.54 ± 0.02aB  0.29 ± 0.02aB  406.4 ± 30.9aB  1.06 ± 0.03bB  0.30 ± 0.01bB  0.77 ± 0.01aB  eJLNMH  21.2 ± 0.45aB  11.0 ± 1.22aB  0.67 ± 0.01bA  0.34 ± 0.02bA  572.6 ± 27.1bA  2.70 ± 0.02aA  1.00 ± 0.01aA  1.70 ± 0.01aA  aJLNMH  20.2 ± 0.84bB  9.8 ± 0.45aB  0.76 ± 0.02aA  0.39 ± 0.01aA  621.0 ± 30.2aA  1.86 ± 0.03bA  0.72 ± 0.01bA  1.14 ± 0.02bA  2015  eLamar  23.8 ± 0.45aA  13.2 ± 0.45aA  0.51 ± 0.04bB  0.25 ± 0.01bB  336.0 ± 19.8bB  1.25 ± 0.08aB  0.45 ± 0.04aB  0.80 ± 0.03aB  aLamar  22.2 ± 0.84bA  12.4 ± 0.55bA  0.55 ± 0.02aB  0.28 ± 0.02aB  381.6 ± 30.1aB  1.07 ± 0.07bB  0.31 ± 0.04bB  0.76 ± 0.03aB  eJLNMH  21.0 ± 0.71aB  11.4 ± 1.14aB  0.65 ± 0.04bA  0.35 ± 0.02aA  557.0 ± 26.8bA  2.76 ± 0.09aA  1.00 ± 0.04aA  1.76 ± 0.05aA  aJLNMH  20.8 ± 0.84aB  10.2 ± 1.10aB  0.77 ± 0.02aA  0.37 ± 0.04aA  634.8 ± 57.9aA  1.87 ± 0.04bA  0.75 ± 0.02bA  1.12 ± 0.02bA  View Large Table 4. Effects of elevated CO2 on the growth, development and reproduction, feeding and excretion of S. litura fed on resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean grown under ambient and elevated CO2 in 2013–2015 (Mean ± SD) Year  Treatment  Larval life span (day)  Pupal life span (day)  Larval weight (g)  Pupal weight (g)  Fecundity (eggs laid/female)  Feeding amount (dry weight; g/larva)  Excretion amount (dry weight; g/larva)  Net consumption (dry weight; g/larva)  2013  eLamar  23.6 ± 0.55aA  13.4 ± 0.55aA  0.48 ± 0.03bB  0.25 ± 0.04aB  306.6 ± 60.7bB  1.22 ± 0.03aB  0.43 ± 0.02aB  0.79 ± 0.02aB  aLamar  21.8 ± 0.45bA  13.0 ± 0.71aA  0.56 ± 0.02aB  0.29 ± 0.02aB  381.4 ± 23.6aB  1.05 ± 0.06bB  0.30 ± 0.03bB  0.75 ± 0.03aB  eJLNMH  21.4 ± 0.55aB  10.8 ± 1.30aB  0.63 ± 0.03bA  0.35 ± 0.04aA  593.6 ± 17.2bA  2.62 ± 0.11aA  1.01 ± 0.05aA  1.61 ± 0.06aA  aJLNMH  20.6 ± 0.55aB  10.0 ± 0.71aB  0.78 ± 0.04aA  0.35 ± 0.03aA  652.8 ± 29.8aA  1.87 ± 0.06bA  0.73 ± 0.03bA  1.14 ± 0.03bA  2014  eLamar  23.2 ± 0.84aA  13.2 ± 0.45aA  0.50 ± 0.01bB  0.24 ± 0.03bB  342.0 ± 20.2bB  1.23 ± 0.13aB  0.43 ± 0.05aB  0.80 ± 0.08aB  aLamar  21.4 ± 0.55bA  12.4 ± 0.55bA  0.54 ± 0.02aB  0.29 ± 0.02aB  406.4 ± 30.9aB  1.06 ± 0.03bB  0.30 ± 0.01bB  0.77 ± 0.01aB  eJLNMH  21.2 ± 0.45aB  11.0 ± 1.22aB  0.67 ± 0.01bA  0.34 ± 0.02bA  572.6 ± 27.1bA  2.70 ± 0.02aA  1.00 ± 0.01aA  1.70 ± 0.01aA  aJLNMH  20.2 ± 0.84bB  9.8 ± 0.45aB  0.76 ± 0.02aA  0.39 ± 0.01aA  621.0 ± 30.2aA  1.86 ± 0.03bA  0.72 ± 0.01bA  1.14 ± 0.02bA  2015  eLamar  23.8 ± 0.45aA  13.2 ± 0.45aA  0.51 ± 0.04bB  0.25 ± 0.01bB  336.0 ± 19.8bB  1.25 ± 0.08aB  0.45 ± 0.04aB  0.80 ± 0.03aB  aLamar  22.2 ± 0.84bA  12.4 ± 0.55bA  0.55 ± 0.02aB  0.28 ± 0.02aB  381.6 ± 30.1aB  1.07 ± 0.07bB  0.31 ± 0.04bB  0.76 ± 0.03aB  eJLNMH  21.0 ± 0.71aB  11.4 ± 1.14aB  0.65 ± 0.04bA  0.35 ± 0.02aA  557.0 ± 26.8bA  2.76 ± 0.09aA  1.00 ± 0.04aA  1.76 ± 0.05aA  aJLNMH  20.8 ± 0.84aB  10.2 ± 1.10aB  0.77 ± 0.02aA  0.37 ± 0.04aA  634.8 ± 57.9aA  1.87 ± 0.04bA  0.75 ± 0.02bA  1.12 ± 0.02bA  Year  Treatment  Larval life span (day)  Pupal life span (day)  Larval weight (g)  Pupal weight (g)  Fecundity (eggs laid/female)  Feeding amount (dry weight; g/larva)  Excretion amount (dry weight; g/larva)  Net consumption (dry weight; g/larva)  2013  eLamar  23.6 ± 0.55aA  13.4 ± 0.55aA  0.48 ± 0.03bB  0.25 ± 0.04aB  306.6 ± 60.7bB  1.22 ± 0.03aB  0.43 ± 0.02aB  0.79 ± 0.02aB  aLamar  21.8 ± 0.45bA  13.0 ± 0.71aA  0.56 ± 0.02aB  0.29 ± 0.02aB  381.4 ± 23.6aB  1.05 ± 0.06bB  0.30 ± 0.03bB  0.75 ± 0.03aB  eJLNMH  21.4 ± 0.55aB  10.8 ± 1.30aB  0.63 ± 0.03bA  0.35 ± 0.04aA  593.6 ± 17.2bA  2.62 ± 0.11aA  1.01 ± 0.05aA  1.61 ± 0.06aA  aJLNMH  20.6 ± 0.55aB  10.0 ± 0.71aB  0.78 ± 0.04aA  0.35 ± 0.03aA  652.8 ± 29.8aA  1.87 ± 0.06bA  0.73 ± 0.03bA  1.14 ± 0.03bA  2014  eLamar  23.2 ± 0.84aA  13.2 ± 0.45aA  0.50 ± 0.01bB  0.24 ± 0.03bB  342.0 ± 20.2bB  1.23 ± 0.13aB  0.43 ± 0.05aB  0.80 ± 0.08aB  aLamar  21.4 ± 0.55bA  12.4 ± 0.55bA  0.54 ± 0.02aB  0.29 ± 0.02aB  406.4 ± 30.9aB  1.06 ± 0.03bB  0.30 ± 0.01bB  0.77 ± 0.01aB  eJLNMH  21.2 ± 0.45aB  11.0 ± 1.22aB  0.67 ± 0.01bA  0.34 ± 0.02bA  572.6 ± 27.1bA  2.70 ± 0.02aA  1.00 ± 0.01aA  1.70 ± 0.01aA  aJLNMH  20.2 ± 0.84bB  9.8 ± 0.45aB  0.76 ± 0.02aA  0.39 ± 0.01aA  621.0 ± 30.2aA  1.86 ± 0.03bA  0.72 ± 0.01bA  1.14 ± 0.02bA  2015  eLamar  23.8 ± 0.45aA  13.2 ± 0.45aA  0.51 ± 0.04bB  0.25 ± 0.01bB  336.0 ± 19.8bB  1.25 ± 0.08aB  0.45 ± 0.04aB  0.80 ± 0.03aB  aLamar  22.2 ± 0.84bA  12.4 ± 0.55bA  0.55 ± 0.02aB  0.28 ± 0.02aB  381.6 ± 30.1aB  1.07 ± 0.07bB  0.31 ± 0.04bB  0.76 ± 0.03aB  eJLNMH  21.0 ± 0.71aB  11.4 ± 1.14aB  0.65 ± 0.04bA  0.35 ± 0.02aA  557.0 ± 26.8bA  2.76 ± 0.09aA  1.00 ± 0.04aA  1.76 ± 0.05aA  aJLNMH  20.8 ± 0.84aB  10.2 ± 1.10aB  0.77 ± 0.02aA  0.37 ± 0.04aA  634.8 ± 57.9aA  1.87 ± 0.04bA  0.75 ± 0.02bA  1.12 ± 0.02bA  View Large Compared with susceptible soybean, resistant soybean significantly prolonged the larval and pupal life span of S. litura in 2013 (Ambient CO2: +5.83 and +30.00%; Elevated CO2: +10.28 and +24.07%), 2014 (Ambient CO2: +5.94 and +26.53%; Elevated CO2: +9.43 and +20.00%), and 2015 (Ambient CO2: +6.73 and +21.57%; Elevated CO2: +13.33 and +15.79%) respectively (P < 0.05; Table 4), and significantly reduced the larval and pupal weight, fecundity, feeding and excretion amount per larva, and net consumption per larva of S. litura in 2013 (Ambient CO2: −28.21, −17.14, −41.57, −43.85, −58.90, and −34.21%; Elevated CO2: −23.81, −28.57, −48.35, −53.44, −57.43, and −50.93%), 2014 (Ambient CO2: −28.95, −25.64, −34.56, −43.01, −58.33, and −32.46%; Elevated CO2: −25.37, −29.41, −40.27, −54.44, −57.00, and −52.94%), and 2015 (Ambient CO2: −28.57, −24.32, −39.89, −42.78, −58.67, and −32.14%; Elevated CO2: −21.54, −28.57, −39.68, −54.71, −55.00, and −54.55%) respectively (P < 0.05; Table 4). Effects of the Interaction Between Soybean Cultivar and CO2 Concentration on the Foliar Chemistry and Yield of Soybean The foliar sugar content and C/N ratio at R4 and R6 stages of soybean (P < 0.01 or 0.001; Table 2), and the seeds weight per plant (P < 0.001; Table 2) were significantly affected by the interaction between CO2 levels and soybean cultivars. Moreover, there was a significant interaction between sampling years and soybean cultivars on the seeds weight per plant (P < 0.05; Table 2). Although the foliar sugar content and C/N ratio of resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean cultivars increased with elevated CO2. However, there was a significant difference in the increment, foliar sugar content in eLamar compared with aLamar increased more than that of eJLNMH compared with aJLNMH, and the increment was more than twice both at R4 (+131.06%) and R6 (+130.43%) stages, similar difference was also found in C/N ratio (R4: +126.26%; R6: +102.74%) (Table 3). Moreover, the seeds weight per plant of eLamar increased significantly in the three sampling years, but the increase of eJLNMH was not so obvious, just in 2014 increased significantly (Fig. 1). Effects of the Interaction Between Soybean Cultivar and CO2 Concentration on the Growth, Development, and Consumption of S. litura The larval life span, larval weight, feeding and excretion amount per larva, and net consumption per larva were significantly affected by the interaction between CO2 levels and soybean cultivars (P < 0.01 or 0.001; Table 2). Moreover, there was significant interaction between sampling years and CO2 levels on the larval weight (P < 0.05; Table 2) and net consumption per larva (P < 0.01; Table 2), and there was significant interaction between sampling years and soybean cultivars on the fecundity (P < 0.05; Table 2), and there was significant interaction among sampling years, CO2 levels, and soybean cultivars on the net consumption (P < 0.01; Table 2). The larval life span of S. litura fed on eLamar was significantly prolonged compared with aLamar in the three sampling years, but the larval life span of S. litura fed on eJLNMH was significantly prolonged compared with aJLNMH just in 2014, and the decrement of larval weight fed on eLamar was less than 25% of the decrement of S. litura fed on eJLNMH in the three sampling years (2013: −25.69%; 2014: −37.42%; 2015: −53.34%) (Table 4). Moreover, the increment of feeding amount per larva of S. litura fed on eLamar was less than 50% of the increment of S. litura fed on eJLNMH in the three sampling years (2013: −59.64%; 2014: −64.48%; 2015: −64.66%), and the increment of excretion amount per larva of S. litura fed on eLamar was more than 10% of the increment of S. litura fed on eJLNMH in the three sampling years (2013: +12.96%; 2014: +11.42%; 2015: +35.49%) (Table 4). Furthermore, the net consumption of S. litura fed on eLamar was insignificant compared with aLamar in the three sampling years, but the eJLNMH significantly increased more than 40% compared with aJLNMH in the three sampling years (Table 4). Correlation Analysis Between the Foliar Chemistry of Soybean and the Growth Indexes of S. litura in Different of CO2 Levels and Sampling Years The foliar sugar content of resistant soybean Lamar and susceptible soybean JLNMH in different of CO2 levels (elevated vs. ambient) and sampling years (2013, 2014, and 2015) was significantly positive correlated with the foliar C/N ratio of soybean, the larval and pupal life span, feeding and excretion amount per larva, and net consumption per larva of S. litura, and was significantly negative correlated with the foliar N content of soybean, the larval weight, pupal weight (except susceptible soybean JLNMH), and fecundity of S. litura (Table 5). The correlation between the foliar C/N ratio of soybean and the growth indexes of S. litura was similar to that of the foliar sugar content and the growth indexes of S. litura (Table 5). The correlation between the foliar N content of soybean and the growth indexes of S. litura was opposite with the first two (Table 5). Table 5. Correlation analysis between the measured indexes of foliar chemistry of soybean and the growth of S. litura fed on resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean grown under ambient and elevated CO2 in 2013, 2014 and 2015 Correlation analysis  Foliar sugar  Foliar nitrogen  Foliar C/N ratio  Larval life span  Pupal life span  Larval weight  Pupal weight  Fecundity  Feeding amount  Excretion amount  Net consumption  Foliar sugar    −0.98‡  0.99‡  0.92†  0.81*  −0.93†  −0.99‡  −0.88*  0.98‡  0.98‡  0.96†  Foliar nitrogen  −0.96†    −0.99‡  −0.96†  −0.87*  0.89*  0.99‡  0.93†  −0.97†  −0.98‡  −0.90*  Foliar C/N ratio  0.99‡  −0.99‡    0.94†  0.85*  −0.90*  −0.99‡  −0.89*  0.98‡  0.98‡  0.94†  Larval life span  0.84*  −0.94†  0.90*    0.81  −0.86*  −0.94†  −0.94†  0.96†  0.98‡  0.86*  Pupal life span  0.94†  −0.93†  0.95†  0.79    −0.74  −0.80  −0.89*  0.80  0.82*  0.67  Larval weight  −0.98‡  0.91*  −0.95†  −0.83*  −0.88*    0.92†  0.89*  −0.92*  −0.91*  −0.90*  Pupal weight  −0.61  0.76  −0.72  −0.74  −0.65  0.54    0.90*  −0.98‡  −0.98‡  −0.94†  Fecundity  −0.93†  0.82*  −0.88*  −0.61  −0.92*  0.88*  0.40    −0.88*  −0.91*  −0.75  Feeding amount  1.00‡  −0.96†  0.99‡  0.82*  0.96†  −0.96†  −0.66  −0.93†    1.00‡  0.97†  Excretion amount  1.00‡  −0.97†  0.99‡  0.88*  0.93†  −0.98‡  −0.67  −0.89*  0.99‡    0.94†  Net consumption  0.99‡  −0.94†  0.98‡  0.78  0.96†  −0.95†  −0.65  −0.95†  1.00‡  0.98‡    Correlation analysis  Foliar sugar  Foliar nitrogen  Foliar C/N ratio  Larval life span  Pupal life span  Larval weight  Pupal weight  Fecundity  Feeding amount  Excretion amount  Net consumption  Foliar sugar    −0.98‡  0.99‡  0.92†  0.81*  −0.93†  −0.99‡  −0.88*  0.98‡  0.98‡  0.96†  Foliar nitrogen  −0.96†    −0.99‡  −0.96†  −0.87*  0.89*  0.99‡  0.93†  −0.97†  −0.98‡  −0.90*  Foliar C/N ratio  0.99‡  −0.99‡    0.94†  0.85*  −0.90*  −0.99‡  −0.89*  0.98‡  0.98‡  0.94†  Larval life span  0.84*  −0.94†  0.90*    0.81  −0.86*  −0.94†  −0.94†  0.96†  0.98‡  0.86*  Pupal life span  0.94†  −0.93†  0.95†  0.79    −0.74  −0.80  −0.89*  0.80  0.82*  0.67  Larval weight  −0.98‡  0.91*  −0.95†  −0.83*  −0.88*    0.92†  0.89*  −0.92*  −0.91*  −0.90*  Pupal weight  −0.61  0.76  −0.72  −0.74  −0.65  0.54    0.90*  −0.98‡  −0.98‡  −0.94†  Fecundity  −0.93†  0.82*  −0.88*  −0.61  −0.92*  0.88*  0.40    −0.88*  −0.91*  −0.75  Feeding amount  1.00‡  −0.96†  0.99‡  0.82*  0.96†  −0.96†  −0.66  −0.93†    1.00‡  0.97†  Excretion amount  1.00‡  −0.97†  0.99‡  0.88*  0.93†  −0.98‡  −0.67  −0.89*  0.99‡    0.94†  Net consumption  0.99‡  −0.94†  0.98‡  0.78  0.96†  −0.95†  −0.65  −0.95†  1.00‡  0.98‡    Foliar sugar and N contents, and C/N ratio are average of R4 and R6 stages in the same year for the same CO2 level. The right triangle (and the left triangle) is the correlation analysis between the measured indexes of foliar chemistry of resistant soybean Lamar (and susceptible soybean JLNMH) and the growth of S. litura in different of CO2 levels (elevated vs. ambient) and sampling years (2013, 2014, and 2015). Pearson correlation coefficient, N = 6; Prob > |r| under H0: Rho = 0. *P < 0.05, †P < 0.01, ‡P < 0.001. View Large Table 5. Correlation analysis between the measured indexes of foliar chemistry of soybean and the growth of S. litura fed on resistant (cv. Lamar) and susceptible (cv. JLNMH) soybean grown under ambient and elevated CO2 in 2013, 2014 and 2015 Correlation analysis  Foliar sugar  Foliar nitrogen  Foliar C/N ratio  Larval life span  Pupal life span  Larval weight  Pupal weight  Fecundity  Feeding amount  Excretion amount  Net consumption  Foliar sugar    −0.98‡  0.99‡  0.92†  0.81*  −0.93†  −0.99‡  −0.88*  0.98‡  0.98‡  0.96†  Foliar nitrogen  −0.96†    −0.99‡  −0.96†  −0.87*  0.89*  0.99‡  0.93†  −0.97†  −0.98‡  −0.90*  Foliar C/N ratio  0.99‡  −0.99‡    0.94†  0.85*  −0.90*  −0.99‡  −0.89*  0.98‡  0.98‡  0.94†  Larval life span  0.84*  −0.94†  0.90*    0.81  −0.86*  −0.94†  −0.94†  0.96†  0.98‡  0.86*  Pupal life span  0.94†  −0.93†  0.95†  0.79    −0.74  −0.80  −0.89*  0.80  0.82*  0.67  Larval weight  −0.98‡  0.91*  −0.95†  −0.83*  −0.88*    0.92†  0.89*  −0.92*  −0.91*  −0.90*  Pupal weight  −0.61  0.76  −0.72  −0.74  −0.65  0.54    0.90*  −0.98‡  −0.98‡  −0.94†  Fecundity  −0.93†  0.82*  −0.88*  −0.61  −0.92*  0.88*  0.40    −0.88*  −0.91*  −0.75  Feeding amount  1.00‡  −0.96†  0.99‡  0.82*  0.96†  −0.96†  −0.66  −0.93†    1.00‡  0.97†  Excretion amount  1.00‡  −0.97†  0.99‡  0.88*  0.93†  −0.98‡  −0.67  −0.89*  0.99‡    0.94†  Net consumption  0.99‡  −0.94†  0.98‡  0.78  0.96†  −0.95†  −0.65  −0.95†  1.00‡  0.98‡    Correlation analysis  Foliar sugar  Foliar nitrogen  Foliar C/N ratio  Larval life span  Pupal life span  Larval weight  Pupal weight  Fecundity  Feeding amount  Excretion amount  Net consumption  Foliar sugar    −0.98‡  0.99‡  0.92†  0.81*  −0.93†  −0.99‡  −0.88*  0.98‡  0.98‡  0.96†  Foliar nitrogen  −0.96†    −0.99‡  −0.96†  −0.87*  0.89*  0.99‡  0.93†  −0.97†  −0.98‡  −0.90*  Foliar C/N ratio  0.99‡  −0.99‡    0.94†  0.85*  −0.90*  −0.99‡  −0.89*  0.98‡  0.98‡  0.94†  Larval life span  0.84*  −0.94†  0.90*    0.81  −0.86*  −0.94†  −0.94†  0.96†  0.98‡  0.86*  Pupal life span  0.94†  −0.93†  0.95†  0.79    −0.74  −0.80  −0.89*  0.80  0.82*  0.67  Larval weight  −0.98‡  0.91*  −0.95†  −0.83*  −0.88*    0.92†  0.89*  −0.92*  −0.91*  −0.90*  Pupal weight  −0.61  0.76  −0.72  −0.74  −0.65  0.54    0.90*  −0.98‡  −0.98‡  −0.94†  Fecundity  −0.93†  0.82*  −0.88*  −0.61  −0.92*  0.88*  0.40    −0.88*  −0.91*  −0.75  Feeding amount  1.00‡  −0.96†  0.99‡  0.82*  0.96†  −0.96†  −0.66  −0.93†    1.00‡  0.97†  Excretion amount  1.00‡  −0.97†  0.99‡  0.88*  0.93†  −0.98‡  −0.67  −0.89*  0.99‡    0.94†  Net consumption  0.99‡  −0.94†  0.98‡  0.78  0.96†  −0.95†  −0.65  −0.95†  1.00‡  0.98‡    Foliar sugar and N contents, and C/N ratio are average of R4 and R6 stages in the same year for the same CO2 level. The right triangle (and the left triangle) is the correlation analysis between the measured indexes of foliar chemistry of resistant soybean Lamar (and susceptible soybean JLNMH) and the growth of S. litura in different of CO2 levels (elevated vs. ambient) and sampling years (2013, 2014, and 2015). Pearson correlation coefficient, N = 6; Prob > |r| under H0: Rho = 0. *P < 0.05, †P < 0.01, ‡P < 0.001. View Large Discussion Effects of Elevated CO2 on Resistant and Susceptible Soybean Elevated CO2 caused increase in aboveground biomass, foliar sugar content and C/N ratio, and reduction in root/shoot ratio (but not significant) and foliar nitrogen content in both resistant and susceptible soybean, confirming the results of other studies (Poorter 1993, Johns and Hughes 2002, Chen et al. 2005). In general, the present atmospheric CO2 concentration is unsaturated for plant photosynthesis (Su et al. 2016). In theory, the increase of atmospheric CO2 concentration has a ‘fertilizer effect’ on plant growth, especially photosynthesis and productivity of the C3 plants (such as wheat, rice, soybean, cotton, etc.) can be improved by the fertilizer effect (Rogers and Dahlman 1993, Rogers et al. 1994), which is conducive to plant growth. Accumulation of nonstructural carbohydrates increased foliar sugars and the C/N ratio and simultaneously decreased foliar N under elevated CO2 (Kimball et al. 1994, Lindroth et al. 1995). The seeds weight of resistant soybean Lamar increased significantly in the three sampling years under elevated CO2, but the increase of susceptible soybean JLNMH was not so obvious. Moreover, the interaction between CO2 levels and soybean cultivars had significant effects on the sugar content and C/N ratio. Foliar sugar content in soybean Lamar increased more than that of the susceptible soybean JLNMH under elevated CO2, and the increment was more than twice, similar difference was also found in C/N ratio. These differences between the resistant soybean and susceptible soybean may due to the characteristics of PI229358 soybean, Tester (1977) found that the resistant soybean (PI229358) had equivalent soluble carbohydrates and 33% more than the susceptible cultivars, the susceptible cultivars accumulated more total nitrogen and at a faster rate than did the resistant plant introductions. Effects of Resistant Soybean Grown Under Elevated CO2 on the Growth, Development, and Reproduction of S. litura Most herbivorous insects appear to be negatively affected by elevated CO2 because of the reduction in foliar N and increase in foliar C/N ratio (Roth and Lindroth 1995, Ji et al. 2011). According to the analysis of the correlation between foliar chemistry of soybean and the growth indexes of S. litura under elevated CO2 and ambient CO2 and in sampling years (2013, 2014, and 2015), high foliar sugar and low N content, and high foliar C/N ratio were found to be negative to the growth, development, and fecundity of S. litura. The elevated CO2 was confirmed to affect the foliar nutrition of soybean, and then to affect the growth and development of S. litura. Based on the ‘Nutrition compensation hypothesis (NH)’ (Nicolas and Sillans 1989, Pennings et al. 1993), elevated CO2 can indirectly affect the development fitness of herbivores by changing the nutritional components of foliar C/N ratio, above-and belowground biomass, and photosynthetic rate of host plants (Ainsworth and Rogers 2007, Jackson et al. 2009, Zavala et al. 2013). Because nitrogen is the most important limiting resource for phytophagous insects (Mattson 1980), so nitrogen content limits insect growth and development. The reduction in food quality might cause the higher feeding of larvae because of the reduction in protein contents, and the higher foliar C/N ratio under elevated CO2 (Hunter 2001). In this study, 21.92~51.09% increase in foliar C/N ratio, and 8.15~16.20% decrease in N content was observed under elevated CO2, which affected the growth and development of S. litura, increased the consumption and fecal matter, prolonged the life span, reduced the weight and moth fecundity. This is consistent with most of the previous studies (Goverde and Erhardt 2002, Johns and Hughes 2002). In addition, the net consumption of S. litura fed on resistant soybean was insignificant between elevated and ambient CO2, while the susceptible soybean significantly increased more than 40% in elevated CO2 compared with ambient CO2. Moreover, the increment of feeding and excretion amount per larva of S. litura fed on resistant soybean were less than 50% and more than 10% of the increments of S. litura fed on susceptible soybean under elevated CO2. Furthermore, the larval life span of S. litura fed on resistant soybean (cv. Lamar) was prolonged more obvious than that of S. litura fed on susceptible soybean (cv. JLNMH) under elevated CO2. Elden and Kenworthy (1994) found that forliar P content of PI229358 soybean was significantly lower than that of some susceptible soybean, according to the ‘Growth rate hypothesis (GRH)’ (Elser et al. 2003), the change of C: N: P ratio was mainly decided by the changes of P content in organisms (Elser et al. 2000, Vanni et al. 2002), low P content of the host plant tissues would limit the growth and development of herbivorous insect (Schade et al. 2003). Besides, when herbivorous insects fed low favorite food, their consumption decreased and developmental duration was prolonged (Zhu et al. 2005, Zhang et al. 2018). As expected, there was significant year-to-year variation in our field research data. Nevertheless, the study exemplifies the complexities of predicting herbivore responses to future climate conditions, particularly in combination with the highly resistant soybean cultivar. The results clearly indicate that elevated CO2 had promoted the biomass and yield of soybean crops, and had negative effects on development of S. litura. This study supports our hypothesis, it seems that the resistant soybean (cv. Lamar) is likely better in yield performance under the increase of carbon dioxide concentration in the future than the susceptible cultivar JLNMH. Moreover, the resistant soybean (cv. Lamar) seems more adaptable to the future concentration of CO2, embodied in better performance against herbivorous Lepidoptera insect pests feeding with the plant chemistry change. About the improvement of the resistance in cultivar Lamar, we speculate that it might be the difference in the plant secondary metabolites of resistant soybean under elevated CO2, which needs further substantiation. Acknowledgments This research was funded and financially supported by National Key Research and Development Program of China (2017YFD0200400, 2016YFD0100201-22), National Natural Science Foundation of China (ID 31571694, 31272051), the Program for Changjiang Scholars and Innovative Research Team in University (ID PCSIRT_17R55), supported by the Fundamental Research Funds for the Central Universities (ID KYT201801), the Natural Science Foundation of Jiangsu Province Youth Fund (SBK2016043525), the Research Grant from the Innovation Project for Graduate Student of Jiangsu Province (KYLX16-1059), the Innovation Training Program for College Student of Jiangsu Province (201710307006X). References Cited Aldea, M., J. G. Hamilton, J. P. Resti, A. R. Zangerl, M. R. Berenbaum, and E. H. D. Elucia. 2005. Indirect effects of insect herbivory on leaf gas exchange in soybean. Plant. Cell Environ . 28: 402– 411. Google Scholar CrossRef Search ADS   Ainsworth, E. A., and S. P. Long. 2005. What have we learned from 15 years of free-air CO2 enrichment (FACE)? A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO2. New Phytol . 165: 351– 371. Google Scholar CrossRef Search ADS PubMed  Ainsworth, E. A., and A. Rogers. 2007. The response of photosynthesis and stomatal conductance to rising [CO2]: mechanisms and environmental interactions. Plant. Cell Environ . 30: 258– 270. Google Scholar CrossRef Search ADS PubMed  Ainsworth, E. A., A. Rogers, A. D. Leakey, L. E. Heady, Y. Gibon, M. Stitt, and U. Schurr. 2007. Does elevated atmospheric [CO2] alter diurnal C uptake and the balance of C and N metabolites in growing and fully expanded soybean leaves? J. Exp. Bot . 58: 579– 591. Google Scholar CrossRef Search ADS PubMed  Ainsworth, E. A., C. R. Yendrek, S. Sitch, W. J. Collins, and L. D. Emberson. 2012a. The effects of tropospheric ozone on net primary productivity and implications for climate change. Annu. Rev. Plant Biol . 63: 637– 661. Google Scholar CrossRef Search ADS   Ainsworth, E. A., C. R. Yendrek, J. A. Skoneczka, and S. P. Long. 2012b. Accelerating yield potential in soybean: potential targets for biotechnological improvement. Plant. Cell Environ . 35: 38– 52. Google Scholar CrossRef Search ADS   Armes, N. J., J. A. Wightman, D. R. Jadhav, and G. V. R. Rao. 1997. Status of insecticide resistance in Spodoptera litura in Andhra Pradesh, India. Pestic. Sci . 50: 240– 248. Google Scholar CrossRef Search ADS   Bazzaz, F. A. 1990. The responses of natural ecosystems to the rising global CO2 levels. Annu. Rev. Ecol. Syst . 21: 167– 196. Google Scholar CrossRef Search ADS   Casteel, C. L., O. K. Niziolek, A. D. B. Leakey, M. R. Berenbaum, and E. H. Delucia. 2012. Effects of elevated CO2, and soil water content on phytohormone transcript induction in Glycine max, after Popillia japonica, feeding. Arthropod Plant Interact . 6: 439– 447. Google Scholar CrossRef Search ADS   Chen, F. J., and F. Ge. 2004. A climatic chamber for controlling CO2 concentration- CDCC-1 chamber. Entomol. Knowledg . 41: 279– 281. Chen, F. J., G. Wu, F. Ge, M. N. Parajulee, and R. B. Shrestha. 2005. Effects of elevated CO2 and transgenic Bt cotton on plant chemistry, performance, and feeding of an insect herbivore, the cotton bollworm. Entomol. Exp. Appl . 115: 341– 350. Google Scholar CrossRef Search ADS   Chen, F. J., Z. H. Dang, and G. J. Wan. 2011. An open-top chamber and experimental facility suitable for simulating the greenhouse effect: China. 201120042889, 1[P]. Chen, X., B. Vosman, R. G. Visser, R. A. van der Vlugt, and C. Broekgaarden. 2012. High throughput phenotyping for aphid resistance in large plant collections. Plant Methods . 8: 33. Google Scholar CrossRef Search ADS PubMed  Coley, P. D. 1998. Possible effects of climate change on plant/ herbivore interactions in moist tropical forests. Clim. Change  39: 455– 472. Google Scholar CrossRef Search ADS   Deng, X. Y., X. C. Wang, W. Y. Yang, and Q. Zhang. 2012. Effect of nitrogen strategies on carbon and nitrogen metabolism of maize in wheat/maize/soybean relay intercropping system. Acta Prataculture Sinica . 21: 52– 61. Deng, P., W. H. Ma, and G. Q. Li. 2015. Age-and nutrition-related cannibalism in larvae of the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae). Acta Entomologica Sinica . 58: 175– 180. Drake, B. G., M. A. Gonzalez-Meler, and S. P. Long. 1997. More efficient plants: a consequence of rising atmospheric CO2? Annu. Rev. Plant Physiol. Plant Mol. Biol . 48: 609– 639. Google Scholar CrossRef Search ADS PubMed  Elden, T. C., and W. J. Kenworthy. 1994. Foliar nutrient concentrations of insect susceptible and resistant soybean germplasm. Corp Sci . 34: 695– 699. Google Scholar CrossRef Search ADS   Elser, J. J., W. F. Fagan, R. F. Denno, D. R. Dobberfuhl, A. Folarin, A. Huberty, S. Interlandi, S. S. Kilham, E. McCauley, K. L. Schulz,et al.   2000. Nutritional constraints in terrestrial and freshwater food webs. Nature  408: 578– 580. Google Scholar CrossRef Search ADS PubMed  Elser, J. J., K. Acharya, M. Kyle, J. Cotner, W. Makino, T. Markow, T. Watts, S. Hobbie, W. Fagan, J. Schade, J. Hood, and R. W. Sterner. 2003. Growth rate–stoichiometry couplings in diverse biota. Ecol. Lett . 6: 936– 943. Google Scholar CrossRef Search ADS   EMBRAPA. Centro Nacional de Pesquisa de Solos. 2009. Manual de métodos analyses químicas para avaliação de fertilidade do solo , 2nd ed. Embrapa Informações Tecnológicas, Brasília, Brazil, 627p. Fehr, W. R., C. E. Caviness, D. T. Burmood, and J. S. Pennington. 1971. Stage of development descriptions for soybeans, Glycine max (L.) Merrill. Crop Sci . 11: 929– 931. Google Scholar CrossRef Search ADS   Goverde, M., and A. Erhardt. 2002. Effects of elevated CO2 on development and larval food-preference in the butterfly coenonympha pamphuis (Lepidoptera, Satyridae). Glob. Chang. Biol . 9: 74– 83. Google Scholar CrossRef Search ADS   Hamilton, J. G., O. Dermody, M. Aldea, A. R. Zangerl, A. Rogers, M. R. Berenbaum, and E. H. Delucia. 2005. Anthropogenic changes in tropospheric composition increase susceptibility of soybean to insect herbivory. Environ. Entomol . 34: 479– 485. Google Scholar CrossRef Search ADS   Hartwig, E. E., L. Lambent, and T. C. Kilen. 1990. Registration of soybean cultivar Lamar. Crop Sci . 30: 231. Horie, T., J. T. Baker, and H. Nakagawa. 2000. Crop ecosystem responses to climatic change: rice, pp. 81– 106. In K. R. Reddy and H. F. Hodges (eds.), Climate change and global crop productivity . CABI publishing, Wallingford, United Kingdom. Google Scholar CrossRef Search ADS   Houghton, J. T., Y. Ding, D. J. Griggs, M. Noquer, P. J. van der Linden, and D. Xiaosu. 2001. Climate change 2001: the scientific basis . Cambridge University Press, Cambridge, United Kingdom. Hunter, M. D. 2001. Effects of elevated atmospheric carbon dioxide on insect-plant interactions. Agric. Forest Entomol . 3: 153– 159. Google Scholar CrossRef Search ADS   IPCC. 2014. Impacts, adaptation and vulnerability. Working group II contribution to the fifth assessment report of the intergovernmental panel on climate change, 1132. In C. B. Field, V. R. Barros, D. J. Dokken, K. J. Mach, M. D. Mastrandrea, T. E. Bilir, M. Chatterjee, K. L. Ebi, Y. O. Estrada, R. C. Genova, B. Girma, E. S. Kissel, A. N. Levy, S. MacCracken, P. R. Mastrandrea & L. L. White (eds.). Cambridge, UK: Cambridge University Press. Jackson, R. B., C. W. Cook, J. S. Pippen, and S. M. Palmer. 2009. Increased belowground biomass and soil CO2 fluxes after a decade of carbon dioxide enrichment in a warm-temperate forest. Ecology  90: 3352– 3366. Google Scholar CrossRef Search ADS PubMed  Ji, L. Z., L. L. An, and X. W. Wang. 2011. Growth responses of gypsy moth larvae to elevated CO2: the influence of methods of insect rearing. Insect Sci . 18: 409– 418. Google Scholar CrossRef Search ADS   Johns, C. V., and L. Hughes. 2002. Interactive effects of elevated CO2 and temperature on the leaf-miner Dialectica scalariella Zeller (Lepidoptera: Gracillariidae) in Paterson’s Curse, Echium plantagineum (Boraginaceae). Glob. Chang. Biol . 8: 142– 152. Google Scholar CrossRef Search ADS   Kim, H. Y., M. Lieffering, K. Kobayashi, M. Okada, and M. Shu. 2003. Seasonal changes in the effects of elevated CO2 on rice at three levels of nitrogen supply: a free air CO2 enrichment (face) experiment. Glob. Chang. Biol . 9: 826– 837. Google Scholar CrossRef Search ADS   Kimball, B. A., R. L. Lamorte, R. S. Seay, P. J. Pinter, R. Rokey, D. J. Hunsaker, W. A. Dugas, M. L. Heuer, J. R. Mauney, G. R. Hendrey,et al.   1994. Effects of free-air CO2-enrichment on energy balance and evapotranspiration of cotton. Agric. For. Meteorol . 70: 259– 278. Google Scholar CrossRef Search ADS   Kimball, B. A., K. Kobayashi, and M. Bindi. 2002. Responses of agricultural crops to free-air CO2 enrichment. Adv. Agron . 77: 293– 368. Google Scholar CrossRef Search ADS   Lambert, L., and T. C. Kilen. 1984. Multiple insect resistance in several soybean genotypes. Crop Sci . 24: 887– 890. Google Scholar CrossRef Search ADS   Lindroth, R. L. 2010. Impacts of elevated atmospheric CO2 and O3 on forests: phytochemistry, trophic interactions, and ecosystem dynamics. J. Chem. Ecol . 36: 2– 21. Google Scholar CrossRef Search ADS PubMed  Lindroth, R. L., Wood, S. A., and B. J. Kopper. 2002. Response of quaking aspen genotypes to enriched CO2: foliar chemistry and tussock moth performance. Agricultural and Forest Entomology 4: 315–323. Mattson, W. J. 1980. Herbivory in relation to plant nitrogen content. Annu. Rev. Ecol. Evol. Syst  11: 119– 161. Google Scholar CrossRef Search ADS   Murray, T. J., D. S. Ellsworth, D. T. Tissue, and M. Riegler. 2013. Interactive direct and plant-mediated effects of elevated atmospheric [CO2] and temperature on a eucalypt-feeding insect herbivore. Glob. Chang. Biol . 19: 1407– 1416. Google Scholar CrossRef Search ADS PubMed  Nicolas, G. A., and D. Sillans. 1989. Immediate and latent effects of carbon dioxide on insects. Ann. Rev. Entomol . 34: 97– 116. Google Scholar CrossRef Search ADS   Norby, R. J., E. H. DeLucia, B. Gielen, C. Calfapietra, C. P. Giardina, J. S. King, J. Ledford, H. R. McCarthy, D. J. P. Moore, R. Ceulmans,et al.   2005. Forest response to elevated CO2 is conserved across a broad range of productivity. Proc. Natl. Acad. Sci. USA . 102: 18052– 18056. Google Scholar CrossRef Search ADS   O’Neill, B. F., A. R. Zangerl, O. Dermody, D. D. Bilgin, C. L. Casteel, J. A. Zavala, E. H. DeLucia, and M. R. Berenbaum. 2010. Impact of elevated levels of atmospheric CO2 and herbivory on flavonoids of soybean (Glycine max Linnaeus). J. Chem. Ecol . 36: 35– 45. Google Scholar CrossRef Search ADS PubMed  Pennings, S. C., M. T. Nadeau, and V. J. Paul. 1993. Selectivity and growth of the generalist herbivore dolabella auricularia feeding upon complementary resources. Ecology  74: 879– 890. Google Scholar CrossRef Search ADS   Poorter, H. 1993. Interspecific variation in the growth response of plants to an elevated ambient CO2 concentration. Vegetatio  104: 77– 97. Google Scholar CrossRef Search ADS   Rogers, H. H., and R. C. Dahlman. 1993. Crop responses to CO2, enrichment. Vegetatio  104–105: 117– 131. Google Scholar CrossRef Search ADS   Rogers, H. H., G. B. Runion, and S. V. Krupa. 1994. Plant responses to atmospheric CO2 enrichment with emphasis on roots and the rhizosphere. Environ. Pollut . 83: 155– 189. Google Scholar CrossRef Search ADS PubMed  Roth, S. K., and R. L. Lindroth. 1995. Elevated atmospheric CO2: effects on phytochemistry, insect performance and insect-parasitoid interactions. Glob. Chang. Biol . 1: 173– 182. Google Scholar CrossRef Search ADS   Rowan, G. B., H. R. Boerma, J. N. All, and J. Todd. 1991. Soybean cultivar resistance to defoliating insects. Crop Sci . 31: 678– 682. Schade, J. D., M. Kyle, S. E. Hobbie, W. F. Fagan, and J. J. Elser. 2003. Stoichiometric tracking of soil nutrients by a desert insect herbivore. Ecol. Lett . 6: 96– 101. Google Scholar CrossRef Search ADS   Srinivasa, R. M., D. Manimanjari, M. Vanaja, C.A. Rama Rao, K. Srinivas, V. U. Rao, and B. Venkateswarlu. 2012. Impact of elevated CO2 on tobacco caterpillar, Spodoptera litura on peanut, Arachis hypogea. J. Insect Sci . 12: 1– 10. Stocker, T., Qin, D., Plattner, G., Tignor, M., Allen, S., and Boschung, J., et al. 2013. IPCC, 2013: climate change 2013: the physical science basis. contribution of working group i to the fifth assessment report of the intergovernmental panel on climate change. Comput. Geom. 18: 95–123. Su, Y., Y. F. Zhang, W. Y. Mou, G. N. Xing, and F. J. Chen. 2016. Responses of morphological trait and yield of soybean to elevated atmospheric CO2 concentration and temperature. Acta Ecologica Sinica . 36: 2597– 2606. Tester, C. F. 1977. Constituents of soybean cultivars differing in insect resistance. Phytochemistry  16: 1899– 1901. Google Scholar CrossRef Search ADS   Vanni, M. J., A. S. Flecker, M. James, J. Hood, and J. L. Headworth. 2002. Stoichiometry of nutrient recycling by vertebrates in a tropical stream: linking species identity and ecosystem processes. Ecol. Lett . 5: 285– 293. Google Scholar CrossRef Search ADS   Watson, R. T., M. C. Zinyowera, and R. H. Moss. 1996. Climate change 1995: impacts, adaptations and mitigation of climate change: scientific-technical analysis . Cambridge University Press, Cambridge, United Kingdom. Williams, R. S., D. E. Lincoln, and R. J. Norby. 1998. Leaf age effects of elevated CO2-grown white oak leaves on spring-feeding lepidopterans. Glob. Chang. Biol . 4: 235– 246. Google Scholar CrossRef Search ADS   Wu, Q. J., J. J. Wu, Y. C. Wu, H. Wang, J. Y. Gai, and D. Y. Yu. 2006. Evaluation of resistance of soybean germplasm to cotton worm (Spodopteral litura Fabricius). Soybean Sci . 25: 410– 413. Xing, G., K. Liu, and J. Gai. 2017. A high-throughput phenotyping procedure for evaluation of antixenosis against common cutworm at early seedling stage in soybean. Plant Methods . 13: 66. Google Scholar CrossRef Search ADS PubMed  Zavala, J. A., C. L. Casteel, P. D. Nabity, M. R. Berenbaum, and E. H. DeLucia. 2009. Role of cysteine proteinase inhibitors in preference of Japanese beetles (Popillia japonica) for soybean (Glycine max) leaves of different ages and grown under elevated CO2. Oecologia  161: 35– 41. Google Scholar CrossRef Search ADS PubMed  Zavala, J. A., P. D. Nabity, and E. H. DeLucia. 2013. An emerging understanding of mechanisms governing insect herbivory under elevated CO2. Annu. Rev. Entomol . 58: 79– 97. Google Scholar CrossRef Search ADS PubMed  Zhang, Y. F., Wan G. J., Liu B., Zhang X. G., Xing G. N., and F. J. Chen. 2018. Elevated CO2 and temperature alter development and food utilization of Spodoptera litura fed on resistant soybean. J. Appl. Entomol. 142: 250–262. Zhu, S. Y., and D. L. Hong. 2008. Comparison between two hybrid cultivars of indica rice (Oryza sativa L.) in seed vigor and biochemical traits after aging. Chin. J. Eco Agriculture  16: 396– 400. Google Scholar CrossRef Search ADS   Zhu, J. H., F. P. Zhang, and H. G. Ren. 2005. Development and nutrition of prodenia litura on four food plants. Entomol. Knowledg . 42: 643– 646. Ziska, L. H., O. Namuco, T. Moya, and J. Quilang. 1997. Growth and yield responses of field-grown tropical rice to increasing carbon dioxide and air temperature. Agron. J . 89: 45– 53. Google Scholar CrossRef Search ADS   Zvereva, E. L., and M. V. Kozlov. 2006. Consequences of simultaneous elevation of carbon dioxide and temperature for plant-herbivore interactions: a meta-analysis. Glob. Chang. Biol . 12: 27– 41. Google Scholar CrossRef Search ADS   © The Author(s) 2018. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

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Environmental EntomologyOxford University Press

Published: Apr 25, 2018

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