Plant-soil feedback (PSF) theory has proven to be a particularly useful framework for illustrating the role of the plant microbiome in plant species coexistence and community dynamics. The theory predicts that negative PSF contributes to plant species coexistence through the accumulation of species-specific soil communities that limit plant performance and that positive PSF contributes to the erosion of plant diversity through the accumulation of species-specific soil communities that promote plant performance. One of the major strengths of PSF theory is that the theoretical models are intimately linked to the design of manipulative experiments that allow for the quantification of feedback. Since its formulation 20 years ago, 100s of studies have measured PSF for dozens of plant species. These studies have shown that PSF can explain patterns of plant community structure, plant species invasion, and plant community dynamics during succession. Despite this knowledge, the factors that influence the strength and direction of PSF remain relatively unknown. Here we report results from a meta-analysis of over 1,000 pairwise PSF comparisons where we tested the relative importance of environmental and evolutionary factors that may affect PSF.
Results/Conclusions
We found that plant relatedness and plant origin (native or non-native) were important predictors of PSF. More distantly related plant species had more negative PSF, suggesting PSF may be important for maintaining phylogenetic diversity within communities. As found in other studies, species pairs that contained a non-native plant species had less negative feedback than pairs of native species, suggesting PSF may play a role in plant invasion. We also found evidence that soil pathogens, in particular, play key roles in driving PSF responses. Despite these findings, there is still much unexplained variation in PSF. While no environmental variables were important predictors of PSF, PSF studies have been conducted in a limited number of settings. Explicit tests of how environmental factors influence PSF are needed to better understand how PSF may shift across time and space. We also noted that studies differed widely in their use of PSF metrics, which may lead to incomplete tests of PSF. In addition to the results of the meta-analysis, I will discuss these issues and potential ways forward in empirical PSF research.