Plant-soil feedback, plant species coexistence, and plant community structure: Twenty years of progress integrating theory and experiment

Plant species coexistence and the persistence of high levels of diversity within plant communities has long posed a challenge to ecologists. Stabilizing negative intraspecific interactions relative to interspecific interactions has traditionally been thought to result from high resource use overlap within species; however, the primacy of resource niche partitioning in explaining coexistence of plant species has been questioned. In the past two decades, it has become well established that the plant microbiome, particularly microbes in soil, play an important role in shaping plant community composition and dynamics. The theoretical framework of plant-soil community feedback offers a useful model for viewing and testing the role of the microbiome in plant community dynamics, as it connects microbial dynamics to the outcome of plant-plant interactions. As tests of plant-soil feedback have become increasingly commonplace, the connection of these tests to the theory has become tenuous in some cases. I will review and extend the plant-soil feedback theory and the conditions for microbiome mediation of plant-plant dynamics. And I will then demonstrate the value of this framework in analyzing the outcome of plant-plant interactions.