Understanding how antagonists influence exotic plant success in recipient communities is a central goal in invasion ecology. Exotic plants can escape from specialist antagonists in a new range lacking co-evolved relationships, or accumulate generalist antagonists that already occur there and spillover onto natives. Both scenarios are expected to increase the competitive success of exotic invaders, but we lack empirical tests linking plant-soil feedbacks with competitive success in plant communities. Here, we grew 19 native and 20 exotic plant species in soils cultured by themselves, by another of the 38 species, and in sterile soil. We also grew 160 communities containing subsets of these 39 species and that varied in their proportion of exotic species. Each community was grown in soil cultured by the residents of that community or in soils cultured by eight different species. We characterized fungal communities using meta-barcoding and used network analyses to identify species' roles in communities.
Results/Conclusions
When grown alone, native plants were equally suppressed by their own soil and soil cultured by other species, suggesting natives are equally susceptible to generalists and specialists occurring in the soil microbial community. Exotic plants accumulated strong negative feedbacks in their own soil. However, native plants suffered higher mortality in exotic-compared with native-dominated communities. This occurred even though native plants showed susceptibility to antagonists cultured by themselves and by other species. Further, exotic plants harbored a greater proportion of putative root pathogens than natives, and those pathogens were shared with native plants. Competition was strongest by exotic plants on natives when approximately 30% or more pathogens were shared between them. Exotic plants were more generalist and had more influence in their network roles, indicated by higher closeness centrality and normalized degree, respectively, compared with natives. These data suggest that exotic plants accumulate generalist pathogens that are shared with native plants and those pathogens harm the natives to a greater extent than they harm exotics.