Influence of invasive earthworms (Amynthas spp.) on Wisconsin forest soil microbial communities and soil chemistry

The invasion of Amynthas species complex of earthworms from Asia into North American hardwood forests poses a novel threat to these ecosystems. These species can competitively exclude previously-established earthworms, have novel effects on microbial communities, and influence the structural and chemical composition of soils differently than other earthworm species. However, because prior research has found that earthworm species is an important factor for microbial community composition, Amynthas species may also uniquely affect soil microbial community composition. To address this, we took earthworm and soil samples from 0.5-m quadrats along an active invasion front of Amynthas agrestis and A. tokioensis at the University of Wisconsin-Madison Arboretum. We tested all soil samples for basal metabolic rates, total carbon, and total nitrogen. We also extracted microbial DNA from cast samples, dissected worm guts, and soil samples, and we used high-throughput DNA sequencing to characterize Amynthas species-specific differences in bacterial and fungal community composition. We found that plots that had been occupied by Amynthas for longer than a year had higher total nitrogen, lower C/N, and different communities of soil bacteria and fungi when compared to newly-invaded plots. We also found that Amynthas had species-specific differences in bacterial communities adhered to worm guts and in worm casts. These results suggest that Amynthas species introduce novel assemblages of bacteria and fungi through their casts, and these differences are associated with the species-specific community composition of earthworm guts. These results also suggest that Amynthas species are likely affecting the soil microbial community during invasion.