The Second Wave of Earthworm Invasion: Interspecific Interactions, Soil Microbial Communities, and Carbon Cycling

In temperate soils, earthworms are significant ecosystem engineers. Recent studies of North American earthworms focusing on invasive European species have demonstrated that invasive European earthworms redistribute nutrients in different pools in the soil and accelerate flux rates among the pools, leading to changes in ecosystem functions. In recent years, a group of Asian invasive earthworms, Amynthas, has been widely reported to be invading forests already inhabited by European species in the Mid-Atlantic region, causing a “second wave of invasion” where the soil ecosystem, already modified by European species, is going through another transition. The objective of this thesis is to understand how the invading Asian species affect the European and native earthworms through interspecific interaction and how these interactions alter soil microbial communities and C dynamics. A revised checklist of species and a new key and diagnosis to species in the genera Amynthas, Metaphire, Pithemera and Polypheretima recorded in North America are presented based on published records and inspecting specimens archived at the National Museum of Natural History, Smithsonian Institution, Washington, D.C. Stable isotope data (δ13C and δ15N) from earthworm tissues indicated that Amynthas hilgendorfi, one of the most common Asian invaders, competes with European species for food resources, providing the first direct evidence of interspecific competition in earthworms. Compared to European and native species, A. hilgendorfi has stronger effects on soil microbial communities and C dynamics, leading to reduced bacteria-to-fungi ratio, increased fresh soil organic matter translocation into subsurface soil, and reduced litter C-derived soil respiration. Altogether, through outcompeting European species, modifying soil microbial community structures and altering C dynamics, A. hilgendorfi invasion may shift the ecosystem into an alternative steady state