Author Description

Plants interact with diverse soil microbes that influence plants in profound ways, including by altering plant physiology, fitness, trait expression, stress responses, and interactions with competitors and herbivores. These microbes can also respond rapidly to abiotic and biotic environments through shifts in community composition or the evolution of key taxa, which means their effects on host ecology and evolution are often perfectly confounded with other biotic and abiotic variables. By experimentally manipulating environments and the microbes those environments select for, my work disentangles microbial effects from other environmental effects. In Chapter 1, I identified a mechanism that could generate patterns of microbe-mediated plant acclimation to soil moisture by applying theory on the evolution of cooperation. I found that byproduct benefits, which occur when traits that favor the survival and reproduction of microbes incidentally benefit plant hosts, can promote plant acclimation to soil moisture. In Chapter 2, I showed that microbes can act as cryptic selective agents, generally weakening the effect of stress on natural selection in plants. This suggests that soil microbes may influence the evolutionary trajectory of plant populations in stressful environments. In Chapter 3, I show that microbes can promote adaptive plant plasticity in response to stress and may influence the evolution of plant plasticity by increasing the expression of genetic variation for plasticity and disrupting genetic correlations for plasticity across stress environments. In Chapter 4, I showed that microbe-mediated plant-soil feedbacks can cause negative linkages between genetic diversity and species diversity, suggesting that plant-soil feedback may dampen the negative effects of diversity loss by promoting diversity at other levels of biological organization. Taken together, this dissertation shows that microbial responses to new environments may commonly and cryptically contri