Intermittent water stress favors microbial generalists that better help wheat under drought

Microorganisms can improve plant resistance to drought through various mechanisms such as the production of plant hormones, osmolytes, antioxidants, and exopolysaccharides. It is, however, unclear how previous exposure to water stress affects the functional capacity of the soil microbial community to help plants resist drought. We compared two soils that had either a continuous or intermittent water stress history for almost forty years. We grew wheat in these soils and subjected it to a water stress, after which we collected the rhizosphere soil and shotgun sequenced its metagenome. Wheat growing in the soil with an intermittent water stress history maintained a higher fresh biomass when subjected to water stress. Genes related to resistance to drought were more abundant in the metagenome and more prevalent, diversified, and redundant in the metagenome assembled genomes of the soil with an intermittent water stress history as compared to the soil with a continuous water stress history. We suggest that an intermittent water stress history selects for generalists that are adapted to both low and replete water contents, and that these generalists harbor a larger repertoire of genes beneficial for life under water stress.