Water stress history and wheat genotype modulate rhizosphere microbial response to drought

International audienceDifferent crop genotypes and soils with different water stress histories are known to harbour different microorganisms, but their relative effect on the response of plant-associated microbes to water stress is not known. In a pot experiment, four wheat genotypes (two with recognized drought resistance and two without) were grown in semi-arid soils with different irrigation histories (irrigated and non-irrigated soils) and exposed to four levels of soil water content (ranging from high to low). After one month of exposure to different soil water contents, we examined plant biomass as well as a general (CO2 production) and a specialized (soil uptake of atmospheric H2) functional processes in the rhizosphere. We further measured the abundance of bacteria and fungi in the rhizosphere using real-time PCR. Wheat shoot biomass was lower when growing in non-irrigated soils under low water content. In contrast, under moderate water contents wheat grown in non-irrigated soils had a significantly higher root biomass compared with those grown in irrigated soils. CO2 production did not differ between genotypes and soil irrigation histories under low soil water content. However, we found significantly higher H2 oxidation rates under low water content in the rhizosphere of plants growing in formerly irrigated soil as compared to those grown in formerly non-irrigated soils, although the intensity of the change was genotype-specific. Bacterial abundance was more sensitive to decreasing soil water content than fungal abundance and was mainly influenced by soil water stress history. Taken together, our results highlight that wheat breeding history and soil water stress history differentially influence crop growth performance, a specialized and a general rhizosphere processes, and rhizosphere bacterial and fungal abundance in the face of decreasing soil water content