Four decades of soil water stress history together with host genotype constrain the response of the wheat microbiome to soil moisture.

There is little understanding about how soil water stress history and host genotype influence the response of wheat-associated microbiome under short-term decreases in soil moisture. To address this, we investigated how plant breeding history (four wheat genotypes; two with recognized drought resistance and two without) and soil water stress history (same wheat field soil from Saskatchewan with contrasting long-term irrigation) independently or interactively influenced the response of the rhizosphere, root and leaf bacterial and fungal microbiota to short-term decreases in soil water content (SWC). We used amplicon sequencing (16S rRNA gene for bacteria and ITS region for fungi) to characterize the wheat microbiome. Fungal and bacterial communities responses to short-term decreases in SWC were mainly constrained by soil water stress history, with some smaller, but significant influence of plant genotype. One exception was the leaf-associated fungal communities, for which the largest constraint was genotype, resulting in a clear differentiation of the communities based on the genotype's sensitivity to water stress. Our results clearly indicate that soil legacy does not only affect the response to water stress of the microbes inhabiting the soil, but also of the microorganisms more closely associated with the plant tissues, and even of the plant itself.