Plant fitness in natural environments and agricultural crop yields are influenced by plant-associated microbiota and soil type. The composition and activity of plant microbiota are determined by nutritional (mineral nutrients), metabolic (primary and specialized metabolites), and edaphic (physical, chemical, and biological properties of soil) factors interacting with different plant genotypes. This Research Area investigates the contribution of microbiota to plant performance and edaphic adaptation. RA2 will identify genetic, molecular, and biochemical mechanisms governing the structure, activity, and function of plant-associated microbial communities in the rhizosphere and phyllosphere. The central working hypotheses of RA2 are as follows: (i) metabolic partnership between plants and associated microbes is important for the establishment of interorganismal nutritional networks, and (ii) variation in this metabolic connectivity is a major force underlying edaphic adaptation and plant health. Metabolic models will be developed from analyses of plant-microbe communities growing in different natural soils and environments, and their physiological relevance will be tested and refined using an iterative set of microbiota reconstitution experiments under controlled nutritional perturbations. Central to RA2 is an integrated analysis of the plant microbiota metabolism, taking advantage of reductionist approaches.