Effects of native and non-native earthworms on grassland plant communities and abundance of associated arbuscular mycorrhizal fungi

Non-native earthworm invasions can greatly alter plant communities directly through root consumption, or indirectly, including through effects on arbuscular mycorrhizal (AM) fungi. However, most invasive earthworm research evaluating effects on plants and AM fungi has been conducted in historically earthworm-free regions. We assessed effects of non-native earthworms on plants and AM fungal abundance in a tallgrass prairie in the U.S. Great Plains where native earthworms are present. Specifically, we evaluated if abundance of native, non-native, and total earthworms were associated with native and non-native plant cover, plant biomass and species richness, and relative abundances of intra- and extra-radical AM fungi. We identified 68 non-native (all Aporrectodea spp.) and 451 native (all Diplocardia spp.) earthworms. Abundances of neither native nor non-native earthworms were associated with percent total plant cover, plant biomass, plant species richness, or intra- or inter-radical AM fungal abundance. However, greater numbers of total earthworms were associated with reduced native plant cover and increased non-native plant cover. Our study suggests total abundance of earthworms, but not of non-native species, influences plant community composition in the tallgrass prairie we studied, and that such effects may be driven by mechanisms other than alteration of symbiotic mycorrhizal fungi. As evidenced by the relatively low proportion of non-native individuals, the earthworm invasion in our study area appears to be nascent, yet further effects on soil, microbes, plants, and ecosystem functions could occur if the invasion intensifies. Continued research in tallgrass prairies is crucial for monitoring current and future impacts of non-native earthworms on these endangered ecosystems.