Disturbance reduces the differentiation of mycorrhizal fungal communities in grasslands along a precipitation gradient.

Given that mycorrhizal fungi play key roles in shaping plant communities, greater attention should be focused on factors that determine the composition of mycorrhizal fungal communities and their sensitivity to anthropogenic disturbance. We investigate changes in arbuscular mycorrhizal (AM) fungal community composition across a precipitation gradient in North American grasslands as well as changes occurring with varying degrees of site disturbance that have resulted in invasive plant establishment. We find strong differentiation of AM fungal communities in undisturbed remnant grasslands across the precipitation gradient, whereas communities in disturbed grasslands were more homogeneous. These changes in community differentiation with disturbance are consistent with more stringent environmental filtering of AM fungal communities in undisturbed sites that may also be promoted by more rigid functional constraints imposed on AM fungi by the native plant communities in these areas. The AM fungal communities in eastern grasslands were particularly sensitive to anthropogenic disturbance, with disturbed sites having low numbers of AM fungal operational taxonomic units (OTUs) commonly found in undisturbed sites, and also the proliferation of AM fungal OTUs in disturbed sites. This proliferation of AM fungi in eastern disturbed sites coincided with increased soil phosphorus availability and is consistent with evidence suggesting the fungi represented by these OTUs would provide reduced benefits to native plants. The differentiation of AM fungal communities along the precipitation gradient in undisturbed grasslands but not in disturbed sites is consistent with AM fungi aiding plant adaptation to climate, and suggests they may be especially important targets for conservation and restoration in order to help maintain or re-establish diverse grassland plant communities.