Climate change and plant-microbe interactions: Water-availability influences the effective specialization of a fungal pathogen

Through species-specific effects on plants, pathogens play a key role in structuring plant communities. A change in abiotic context, such as those mediated by climate change, may alter plant communities through changes in the specificity of plant-pathogen interactions. To test how water availability influenced the specificity of plant-pathogen interactions, we grew paired congeners of three native and three nonnative coastal prairie plant species with or without a pathogenic soil fungus, Fusarium incarnatum-equiseti species complex 6 b, under low, average, and high water treatments. Across the plant species tested, the Fusarium treatment had stronger negative and species-specific effects on plant biomass at high water availability than low water availability. If generalizable, our results suggest that stronger and more species-specific pathogen effects could drive changes in plant community composition in wetter conditions, but plant-pathogen interactions may be less important for plant community structure in drier conditions.