Soil microaggregate bacterial communities followingAmynthas tokioensisandAmynthas agrestisearthworm co-invasion

Abstract Earthworms restructure the soil environment through burrowing, consumption, and casting behaviors. Though non-native European Lumbricid earthworms are well-studied in North American soils, the Asian pheretimoid Amynthas tokioensis and Amynthas agrestis earthworms exhibit distinct ecological patterns that alter invaded habitats. In particular, bioturbation may affect soil aggregation and microbial community assembly processes, such as dispersal and selection. We aimed to determine the effects of A. tokioensis and A. agrestis co-invasions in woodlands in Madison, WI, U.S. on soil bacterial communities and edaphic characteristics. Using 16S rRNA gene sequencing, we found that the presence and activity of these Amynthas species earthworms significantly affected bacterial community composition. At one site, there was a decrease in sample-to-sample dissimilarity (i.e., decreased beta diversity), with concomitant increases in homogenizing community assembly processes. However, at the other site, we found opposite trends, with evidence for increased compositional dissimilarity between samples and decreased evidence for homogenizing community assembly processes. Overall, inconclusive support for the hypothesized homogenization of bacterial community composition driven by homogenizing community assembly processes indicates that the effects of Amynthas pressure in these systems represent a departure from previously established soil disturbance paradigms. Instead, we conclude that aggregate formation via A. tokioensis and A. agrestis casting activity does not consistently impose a strong selective filter on soil bacterial communities, nor does the heightened earthworm activity necessarily act to meaningfully homogenize soil communities via dispersal. Overall increases in soil C and N under Amynthas spp. activity support previous work indicating enhanced decomposition and incorporation of soil litter, but future work could focus on long-term fate of microaggregate-protected C.