Plants and animals can adapt to a wide range of abiotic environments, but they often are not doing it alone. Instead, microbial communities respond to abiotic environments in ways that can help maintain plant and animal fitness, a phenomenon known as “microbe-mediated host adaptation.” Prior research by GEMS trainee Lana Bolin showed that byproduct benefits, which occur when the selfish act of one species provides an incidental benefit to another species, can contribute to microbe-mediated host adaptation. However, other mechanisms that result in classic cooperation could also contribute. This project will test whether a mechanism of classic cooperation—partner choice—can contribute to microbe-mediated host adaptation in plants. This work will elucidate how “diffuse” interactions between plants and soil microbes may contribute to adaptive plant responses to environmental change, as well as promote our understanding of how diffuse symbiosis can arise from natural variation in soil microbes.