Effects of Water Availability on Plant Coexistence through Altered Plant-Microbe Interactions

The biotic and abiotic factors that contribute to plant community structure and stability are of great interest to ecologists. A growing body of research suggests that interactions between plants and soil microbes contribute to coexistence within plant communities. The structure and function of the soil microbial community are highly context-dependent, so changes in abiotic factors could affect plant coexistence by altering the soil microbial community. However, few studies have examined this possibility. I conducted two experiments to test how water availability interacts with the soil microbial community to affect 1) the relative importance of interspecific and intraspecific competition between plant species and 2) plant-soil feedback. I centered my studies on plants commonly found in the Texas coastal prairie. I found that the presence of soil microbes increased the strength of intraspecific competition relative to interspecific competition, but their effect depended on water availability. As water availability increased in the presence of microbes, the strength of intraspecific competition decreased. However, this interaction was dependent on plant species identity. I also found that increasing water availability caused plant-soil feedback to increase from weakly negative to positive. The results of both of my studies suggest that interactions between the soil microbial community and increasing water availability could destabilize coexistence in plant communities. As ecosystems continue to experience changes in abiotic conditions due to ongoing anthropogenic climate change, it is essential to understand how those changes affect the interactions between plants and soil microbes in order to more accurately predict how plant community structure and stability will change in the future.