Water Deficit Stress Alters the Microbial Community Assembly, Structure, and Sources in Corn and Sugar Beet.

Plant-associated microbes can improve plant fitness under abiotic stress conditions like drought by providing stress-relieving benefits to the host; however, there is limited research on the complex ways in which microbial communities assemble in plants under varying environmental conditions. In a field study, we examined the bacterial, fungal, and protist communities of the rhizospheres, roots, and leaves of corn and sugar beet grown under irrigated and water deficit conditions. We hypothesised that water deficit would alter the community composition and structure of plant microbiomes by shifting the relative importance of community assembly processes and the patterns of movement from microbial sources to sinks. Using amplicon sequencing and modelling approaches, we found that the water deficit treatment led to key differences in microbial community structure and that these changes were likely driven by differences in community assembly processes and microbial source communities. Altogether, these results indicate that plant microbiome communities are shaped by available microbial sources, host selection factors, microbial interactions, and stochastic forces, and that each of these factors is influenced by osmotic stress. These findings highlight the importance of applying ecological concepts to plant microbiome research in order to elucidate the impacts of environmental factors on microbial community assembly.