Dissecting fine root diameter distribution at the community level captures root morphological diversityErktan, Amandine; Roumet, Catherine; Munoz, François
doi: 10.1111/oik.08907pmid: N/A
Characterizing plant functional diversity is essential to decipher community assembly rules and ecosystem functioning. Most studies focused on above‐ground traits whereas the analysis of root diversity lags far behind. We analyzed the structure of fine root (< 2 mm) diameter distribution at the community level as an indicator of root morphological diversity, and hypothesized that the shape of the distribution provide insights on root types and root exploration strategies. We tested this hypothesis along a successional gradient (6–69 year‐old) with yearly mowing to better understand assembly rules regarding to belowground processes, and explored the relations between the parameters describing its modes and the vegetation composition and ecological properties of plant communities. Most communities showed a multimodal distribution, with two main modes corresponding to absorptive roots (thinner root mode) and transport roots (coarser root mode), and a third mode of lower importance corresponding to large transport roots. In early succession, the thinnest root mode was prominent, reflecting the dominance of thin absorptive roots and a low proportion of transport roots, resulting in a low root morphological diversity. As succession proceeds, the relative proportion of the second mode increased, and the proportions of the two main modes were more balanced, resulting in an increased variance and root morphological diversity. Furthermore, the first root mode (absorptive roots) became wider and shifted from very thin to thicker roots, suggesting the coexistence of various root strategies for resource exploration. Yearly mowing did not affect root diameter distribution, which may relate to the relative low mowing pressure that enabled woody species to remain, with stunted stature. Overall, our study demonstrates that the distribution of fine root diameters sheds light on root morphological diversity at the community level, and provide hints on the co‐existence of root types and strategies for resource use and exploration.
Are fine roots ‘leaves underground' in terms of allometry? A test in a tropical forest successional series in southwest ChinaGuo, Zijian; Miao, Wenhao; Lyu, Yueming; Sun, Han; Fan, Dayong; Wang, Xiangping
doi: 10.1111/oik.09465pmid: N/A
Fine roots have been hypothesized to be ‘leaves underground' in terms of vascular network, but this hypothesis has rarely been tested within the framework of metabolic scaling theory (MST). We measured average fine‐root (diameter < 1 mm) mass (M), surface area (A), volume (V), diameter (D) and length (L) for 216 soil cores from 24 plots across four successional stages in tropical forests of Xishuangbanna (southwest China), and examined eight scaling relationships between these variables at the individual root scale. We tested whether fine‐root allometries conformed to MST's model for leaf (MSTl) or model (MSTw) for woody organs (e.g. trunk). We also assessed the relative effects of environmental factors, tree size, species composition and diversity, and stand structural factors on allometric relationships using structural equation models (SEMs). Our results showed that: 1) fine‐root scaling exponents rarely conformed to MSTl's predictions. 2) The scaling exponents between fine‐root M, A, V and D all conformed to MSTw's predictions in later successional forests, but showed greater deviation towards early successional stage. 3) The scaling exponents associated with fine‐root length differed markedly from MSTw's predictions. 4) Changes of some fine‐root scaling exponents across successional stage were mainly affected by tree size or soil fertility, and species composition affected allometry only indirectly via tree size. Our results suggested that the allometries of individual fine roots largely conform to the scaling rules governing woody organs instead of leaves, probably because leaves are nearly two‐dimensional objects while the other two are three‐dimensional. We showed that MSTw can well predict some fine‐root allometries in later successional forests, suggesting great potential of utilizing MSTw to better estimate fine‐root biomass and productivity. However, the present MSTw still needs to be improved for predicting the scaling relationships concerning fine‐root length, and also for better quantifying allometric exponents in earlier successional forests.
Patterns of belowground overyielding and fine‐root biomass in native and exotic angiosperms and gymnospermsSchuster, Michael J.; Williams, Laura J.; Stefanski, Artur; Bermudez, Raimundo; Belluau, Michaël; Messier, Christian; Paquette, Alain; Gravel, Dominique; Reich, Peter B.
doi: 10.1111/oik.08877pmid: N/A
Mixing tree species can lead to more productive forests, but how belowground productivity is affected by mixtures of trees of diverse phylogenetic and eco‐evolutionary histories is unclear. Here, we examine how species origin and phylogeny affect belowground productivity in tree communities of varied richness and functional diversity. We measured standing fine‐root biomass and annual fine‐root production across 41 assemblages of 12 tree species, representing both angiosperms and gymnosperms originating from North America and Europe. Increasing functional diversity of mixtures stimulated overyielding of annual production but did not affect standing biomass. In general, annual productivity of mixtures of species that were less productive in monoculture had neutral (angiosperms) to positive (North American species: +16%) responses to mixing, whereas annual productivity of mixtures of species that were more productive in monoculture had neutral (European species) to negative (gymnosperms: −6%) responses to mixing. These differences translated into angiosperm mixtures overyielding in standing biomass by 16% but no effects of mixing on gymnosperm mixtures. The trends we observed between North American and European species annual production were reversed when considering standing biomass. European mixtures had 14% more standing biomass and North American mixtures had 10% less standing biomass than expected from monocultures.
Consequences of tropical rainforest conversion to tree plantations on fine root dynamics and functional traitsKotowska, Martyna M.; Samhita, Sasya; Hertel, Dietrich; Triadiati, Triadiati; Beyer, Friderike; Allen, Kara; Link, Roman M.; Leuschner, Christoph
doi: 10.1111/oik.08898pmid: N/A
Despite the crucial role of fine roots for water and nutrient uptake, soil biological activity and ecosystem carbon cycling, the response of root dynamics to rapidly advancing land‐use change in the tropics is still poorly understood. To address this uncertainty, we investigated the consequences of tropical forest conversion to intensively managed tree plantations for a suite of functional fine root traits. We analysed fine root morphology (diameter, specific root length (SRL), tissue density) and chemistry, as well as root lifespans in four prevalent land‐use systems in the lowlands of Sumatra (Indonesia), namely natural forest, jungle rubber, rubber and oil palm monocultures. Fine root production was estimated using three independent approaches (sequential coring, ingrowth cores, mini‐rhizotrons). Contradicting the expected trend from more conservative to more acquisitive fine root traits with increasing land‐use intensity, we found that SRL and tissue density were significantly higher in forest trees, while fine root diameter was largest in rubber trees and root N content lowest in the oil palm system. Median fine root longevity in the top soil was 11% higher in rubber plantations (238 days) than in jungle rubber (211 days), and more than 50% greater than in the forest (140 days) and oil palm plantations (125 days). Fine root production was higher in the forest and oil palm plantations (ranging between 2 and 9 Mg ha−1 year−1) than the rubber stands, but annual totals varied depending on the methodological approach. Conversion of tropical lowland forest to agricultural systems significantly altered community‐level fine root morphology, dynamics and longevity, with likely consequences for soil carbon cycling and soil biological activity. However, land‐use intensification did not consistently lead to more acquisitive fine root systems; rather, differences in root morphology and dynamics were driven by species‐specific root trait syndromes especially of rubber and oil palm.
Repeated extreme droughts decrease root production, but not the potential for post‐drought recovery of root production, in a mesic grasslandSlette, Ingrid J.; Hoover, David L.; Smith, Melinda D.; Knapp, Alan K.
doi: 10.1111/oik.08899pmid: N/A
Global climate change is expected to cause more frequent extreme droughts in many parts of the world. Despite the crucial role of roots in water acquisition and plant survival, our understanding of ecosystem vulnerability to drought is primarily based on aboveground impacts. As return intervals between droughts decrease, root responses to one drought might alter responses to subsequent droughts, but this remains unresolved. We conducted a seven‐year experiment that imposed extreme drought (growing season precipitation reduced 66%) in a mesic grassland. Plots were droughted during years 1–2 (‘Drought 1'), or years 5–6 (‘Drought 2') or both. We quantified root production during year 6 (final year of Drought 2) and year 7 (first year after Drought 2), when all plots received ambient precipitation. We found that repeated drought decreased root mass production more than twice as much as a single drought (−63% versus −27%, respectively, relative to ambient precipitation). Root mass production of the dominant C4 grass Andropogon gerardii did not decrease significantly with either one or two droughts. A. gerardii root traits differed from subdominant species on average across all treatments, but drought did not alter root traits of either A. gerardii or the subdominant species (collectively). In year 6, root production in plots droughted 4 years ago had not recovered (−21% versus control), but root production recovered in all formerly droughted plots in year 7, when precipitation was above average. Our results highlight the complexity of root responses to drought. Drought‐induced reductions in root production can persist for years after drought and repeated drought can reduce production even further, but this does not preclude rapid recovery of root production in a wet year.
No evidence of foliar disease impact on crop root functional strategies and soil microbial communities: what does this mean for organic coffee?Gagliardi, Stephanie; Avelino, Jacques; Fulthorpe, Roberta; Virginio Filho, Elias de Melo; Isaac, Marney E.
doi: 10.1111/oik.08987pmid: N/A
Global climate change is increasing pest and pathogen pressures on plant communities, deteriorating optimal plant functioning. In plant communities, root functional trait expression and microbial communities are important indicators of plant functioning belowground, and, when confronted with pathogens aboveground, can simultaneously reflect plant defence strategies. Yet, while research is continuing to emerge on the response of root functional traits and microbial processes to pathogens aboveground, little work has investigated these interactions in tree‐crops, or the role organic amendments play in moderating these relationships. The main objective of this study is to disentangle the dynamic effects of pathogens and amendments on root functional traits (i.e. specific root length and area, root diameter, root length density, root nitrogen and root carbon to nitrogen ratio) and root endophytic fungal communities. As a model, we use Coffea arabica (coffee) variety Caturra along a gradient of coffee leaf rust – a foliar disease prominent in coffee systems – under contrasting but widespread amendment regimes in biodiverse agroforestry systems. We found that root trait expression varies along established conservation and collaboration gradients, where fungal endophyte community composition varies significantly as a function of root traits. Belowground resource acquisition strategies do not change with foliar disease incidence, suggesting they may be decoupled. Rather, amendment regimes differentially shape root trait expression and microbial communities, where coffee plants under organic amendments, regardless of foliar disease incidence, expressed greater acquisitive traits and enhanced collaboration with symbiotic fungi. This is an important first step in disentangling the dynamic inter‐relationships between plant traits, endophytes and pathogens, generating new questions on the role of amendments in sustainable pathogen management in biodiverse agroecosystems.