Limited water supply is one of the largest impediments to food production worldwide in the light of climate change and increasing food demand. Functional traits of the plant’s rhizosphere have not been explored in relation to their potential role for increasing plant drought tolerance and for improving crops capacity to optimally manage soil water depletion. So far, an optimization of root and rhizosphere hydraulic traits has been rarely considered in plant breeding. Although recent studies hinted towards an intimately tied link between belowground hydraulic conductivities and stomatal regulation under water deficit, the effect of belowground hydraulics on soil-plant water relations remain disputable. The overall objective of this study was to investigate a systematic understanding of the most important rhizosphere traits and the mechanisms by which they support drought resistance.
Therefore, we have exposed a selection of 48 maize (Zea mays L.) varieties, equally consisting of modern hybrids and landraces, to soil water stress in a phenotyping experiment. We measured the relation between leaf xylem water potential, soil water potential, soil water content and transpiration rate, as well the expression of root and rhizosphere traits like root length or rhizosheath mass between genotypes. Our hypothesis is that stomatal response to soil drying is related to a loss in soil hydraulic conductivity and that key root and rhizosphere hydraulic traits affect such relation.
We have found that the genotypes differed in their responsiveness to drought, indicated by the critical soil water content at which plants felt stressed enough to close stomata, and that this is related to a combination of plant hydraulic conductivity, maximum transpiration, and root and rhizosphere biomass. Those findings stress the importance of belowground hydraulic properties on stomatal regulation and thereby drought responsiveness of maize.