Maintenance of Plant Species Diversity by Pathogens

We present strong evidence that pathogens play a critical role in structuring plant communities and maintaining plant diversity. Pathogens mediate plant species coexistence through trade-offs between competitive ability and resistance to pathogens and through pathogen specialiation. Experimental tests of individual plant pathogen interactions, tests of feedback through host-specific changes in soil communities, and field patterns and field experimentation consistently identify pathogens as important to plant species coexistence. These direct tests are supported by observations of the role of pathogens in generating the productivity gains from manipulations of plant diversity and by evidence that escape from native pathogens contributes to success of introduced plant species. Further work is necessary to test the role of pathogen dynamics in large-scale patterns of plant diversity and range limits, the robustness of coexistence to coevolutionary dynamics, the contribution of different pathogens, and the role of pathogens in plant succession.