Direct plant-soil interactions, and those mediated by soil microbial communities, are critical determinants of tree species performance and distributions. Our work focuses on tropical ecosystems, but our research questions are equally applicable across a range of ecosystem types. Our research focuses among others on the ecology and evolution of symbiotic fungi associated with seeds and roots of tropical trees; quantifying, through experiments, their influence on the processes that maintain tropical forest diversity. We apply the tools of microbial ecology (next-generation sequencing, culturing, and manipulative experiments) and biogeochemistry in the context of plant community ecology.