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Wimmer, Monika A.; Goldbach, Heiner E.
doi: 10.1002/jpln.201200006pmid: N/A
Plants in arid or semiarid areas often experience simultaneous salt and boron (B) stress. Interactive effects on stress responses have been clearly established, but results are inconsistent and variably indicate antagonistic or synergistic interactions even within the same plant species. In this study, five differently B‐ and salt‐resistant wheat genotypes were grown hydroponically at low and high B supply. The effect of increasing NaCl salinity on plant growth, boron uptake rates, shoot B concentrations, and transpiration was determined under both B regimes. The interactive effect of salt and B was different under low and high B supply. Boron‐uptake rates were reduced with increasing salt concentration only under high B supply, and reductions correlated significantly with decreases in leaf area and shoot B concentrations. Under low B supply, however, salt‐induced effects on B‐uptake rates were variable and not significantly correlated with leaf‐area reductions. These results suggest that under high B supply, when B uptake is predominantly passive by diffusion or channel‐mediated via aquaporins, transpiration‐driven water flow is the dominant factor for B accumulation in arial plant parts. Under low B supply, when a significant portion of B can be taken up via active pathways, transpiration is not the decisive factor for B accumulation. Under these conditions, the salt sensitivity of a genotype is a modifying factor of salt–B interactions, because salt‐induced growth inhibition can result in a concentration effect, offset the reduction of B‐uptake rates, and result in increased shoot B concentrations. Contradictory reports on the nature of salt–B interactions might in part be related to low levels of B supply chosen as control treatments and concomittant differences in predominant B‐uptake pathways.
Will, Silke; Eichert, Thomas; Fernández, Victoria; Müller, Torsten; Römheld, Volker
doi: 10.1002/jpln.201100107pmid: N/A
Experiments to assess the rate of absorption and translocation of foliar‐applied, isotopically labeled boric acid (BA) were carried out with lychee (Litchi chinensis Sonn.) and soybean (Glycine max (L.) Merr.) plants. Boron (B) absorption and translocation within the plant, one week after treatment, was investigated after adding to the boric acid (BA solutions 0.5 mM CaCl2 and/or 50 or 500 mM sorbitol). The contribution of stomata to the absorption process was assessed by applying the solutions either to the adaxial or to the abaxial leaf side. Both plant species differed greatly in total absorption rates. The adaxial leaf surface (lacking stomata) of lychee leaves was nearly impermeable, while the stomatous abaxial surface was permeable to BA solutions. In this species, no translocation of 10B to other leaf parts and no effect of adjuvants in increasing 10B absorption were recorded. In contrast, 10B was absorbed both by adaxial and abaxial leaf surfaces of soybean leaves. Boron concentrations measured in treated soybean leaves were sixfold higher after application to the abaxial as compared to the adaxial leaf surface. The addition of adjuvants significantly enhanced the rate of 10B absorption, but not its translocation within the plant. Treatments containing 500 mM sorbitol led to increased 10B absorption and enhanced acropetal 10B movement, whereas adding only 50 mM sorbitol had no significant effect. Application of 0.5 mM CaCl2 in combination with 500 mM sorbitol decreased the rate of 10B absorption, compared to the performance of 500 mM sorbitol alone. Basipetal 10B translocation was very limited. A distinct effect of B‐sorbitol complexes on B translocation apart from the pure adjuvant effect could not be discerned in this investigation.
Liakopoulos, Georgios; Psaroudi, Varvara; Stavrianakou, Sotiria; Nikolopoulos, Dimosthenis; Karabourniotis, George
doi: 10.1002/jpln.201100058pmid: N/A
Root active uptake and remobilization of boron (B) have been accepted as mechanisms contributing to nutrient efficiency under low supply of boron. Here, we examined the existence of these mechanisms in eggplant (Solanum melongena L.) supplied either with luxury (100 μM, B+) or low (7.5 μM, B–) B in the growth medium via semihydroponic cultivation. Boron treatment was marginally not limiting growth thus avoiding side‐effects and impairment of acclimation mechanisms of plants. The induction of a B‐concentrating mechanism was evident in the roots as B concentration in the xylem sap was only decreased by 23% in B– compared to B+ plants, i.e., B– roots concentrated B by a factor of 2.7 relative to the external solution. Leaf B concentration in the B– treatment decreased by 33% and 40% in young fully expanded and mature leaves, respectively. Larger differences were observed in the soluble B fraction that decreased by 65% in mature leaves. However, both total and soluble B concentrations in developing leaves were almost equal for both treatments exhibiting a pattern commonly observed in B‐remobilizing plants. On the other hand, amounts of B export in the phloem sap were small compared to other species in which B is highly mobile. The B export rate from source leaves was slightly increased under low B supply while that of sucrose was not affected. We conclude that the root concentrating mechanism contributes to the alleviation of B deficiency in eggplant under low B supply while B remobilization may also contribute to a lower degree.
Rejsek, Klement; Vranova, Valerie; Pavelka, Marian; Formanek, Pavel
doi: 10.1002/jpln.201000139pmid: N/A
Acid phosphomonoesterase (APM) (E.C. 3.1.3.2) in soil is either of plant‐root or microbial origin. Each of these sources may be dominant in certain ecosystems. Generally, extracellular APM in soil has been reported. However, the lack of suitable methods limits investigations of APM in soil. Root‐derived APM comes from intact plant roots, root exudates, root apoplastic sap, root extracts, or mycorrhizal fungi. The significance of these sources of APM is discussed in this review being the highest in intact roots or root extracts, and within wall‐ and membrane‐bound fraction of mycorrhizal fungi. Evaluation of the location of APM has been based on extraction of fractions of APM with different types of extractants. The suitability of individual extractants and lack of these procedures as well as the need to search for other suitable solutions to increase extraction efficiency, minimalize extraction of inhibitors and solubilization of organic compounds are discussed. As APM derived from roots and soil microorganisms show different kinetic properties, and differ in their response to environmental factors, determination of the significance of root and microbial APM within ecosystems requires further research aimed at evaluating the response of P transformation to climatic and other environmental changes.
Sun, Wei; Whelan, Brett M.; Minasny, Budiman; McBratney, Alex B.
doi: 10.1002/jpln.201100005pmid: N/A
Apparent electrical conductivity of soil (ECa) is a property frequently used as a diagnostic tool in precision agriculture, and is measured using vehicle‐mounted proximal sensors. Crop‐yield data, which is measured by harvester‐mounted sensors, is usually collected at a higher spatial density compared to ECa. ECa and crop‐yield maps frequently exhibit similar spatial patterns because ECa is primarily controlled by the soil clay content and the interrelated soil moisture content, which are often significant contributors to crop‐yield potential. By quantifying the spatial relationship between soil ECa and crop yield, it is possible to estimate the value of ECa at the spatial resolution of the crop‐yield data. This is achieved through the use of a local regression kriging approach which uses the higher‐resolution crop‐yield data as a covariate to predict ECa at a higher spatial resolution than would be prudent with the original ECa data alone. The accuracy of the local regression kriging (LRK) method is evaluated against local kriging (LK) and local regression (LR) to predict ECa. The results indicate that the performance of LRK is dependent on the performance of the inherent local regression. Over a range of ECa transect survey densities, LRK provides greater accuracy than LK and LR, except at very low density. Maps of the regression coefficients demonstrated that the relationship between ECa and crop yield varies from year to year, and across a field. The application of LRK to commercial scale ECa survey data, using crop yield as a covariate, should improve the accuracy of the resultant maps. This has implications for employing the maps in crop‐management decisions and building more robust calibrations between field‐gathered soil ECa and primary soil properties such as clay content.
Puhlmann, Heike; von Wilpert, Klaus
doi: 10.1002/jpln.201100139pmid: N/A
The hydraulic properties of soils, i.e., their ability to store and conduct water, mainly govern the availability of soil water for plants. Information on the hydraulic properties is needed, e.g., for the quantification of drought risk at a given site. Furthermore, knowledge of the water transport is the precondition for the estimation of element fluxes in the soil, e.g., when predicting element leaching from the root zone to the groundwater. For forest soils, only few systematic investigations of their hydraulic properties exist. Within the 2nd forest‐soil survey of Germany, soil samples were taken along a regular 8 km × 8 km grid in the forests of the State of Baden‐Württemberg and the hydraulic properties were estimated in the laboratory by multistep outflow experiments. Besides the soil‐hydraulic measurements, numerous additional soil chemical and physical analyses were carried out and comprehensive profile descriptions were compiled and integrated in a hydraulic database. Based on this database, multiple‐linear‐regression techniques were used to develop pedotransfer functions for the water‐retention curve and the unsaturated‐hydraulic‐conductivity curve using the parametric models of Mualem/van‐Genuchten. Our work fills a gap since to our knowledge, no pedotransfer functions for the unsaturated hydraulic conductivity for forest soils exist so far. The predictive accuracy of the established pedotransfer functions, both for the water‐retention curve and the hydraulic‐conductivity curve, is in the range of (and in some cases better than) other published pedotransfer functions that were mostly derived for agricultural soils.
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