Fig. 6.

Proposed model for selection of monoderm lineages during drought in the root-associated microbiome. (1) Early plant root development selects for diderm lineages under normal irrigation. (2) Drought induces shifts in plant root metabolism, including increases in a range of carbohydrates, secondary metabolites, and amino acids. These shifts lead to exudation of these and possibly other metabolites, which, in turn, supports growth of specific lineages. Additionally, negative selection through an as yet unknown mechanism causes decreases in the absolute abundance of all bacteria, but with greater selection against cells with diderm cell wall characteristics. (3) Rewatering leads to a release from metabolite-mediated and other unknown selective pressures, allowing for rapid growth of diderms and a return to the pattern of root microbiome development and activity observed under control conditions.