Effects of non-native Asian earthworm invasion on temperate forest and prairie soils in the Midwestern US.
Effects of invasive European earthworms in North America have been well documented, but less is known about ecological consequences of exotic Asian earthworm invasion, in particular Asian jumping worms (Amynthas) that are increasingly reported. Most earthworm invasion research has focused on forests; some Amynthas spp. are native to Asian grasslands and may thrive in prairies with unknown effects. We conducted an earthworm-addition mesocosm experiment with before-after control-impact (BACI) design and a complementary field study in southern Wisconsin, USA, in 2014 to investigate effects of a newly discovered invasion of two Asian jumping worms (Amynthas agrestis and Amynthas tokioensis) on forest and prairie litter and soil nutrient pools. In both studies, A. agrestis and A. tokioensis substantially reduced surface litter (84-95% decline in foliage litter mass) and increased total carbon, total nitrogen, and available phosphorus in the upper 0-5 cm of soils over the 4-month period from July through October. Soil inorganic nitrogen (ammonium- and nitrate-N) concentration increased across soil depths of 0-25 cm, with greater effects on nitrate-N. Dissolved organic carbon concentration also increased, e.g., 71-108% increase in the mesocosm experiment. Effects were observed in both forest and prairie soils, with stronger effects in forests. Effects were most pronounced late in the growing season when earthworm biomass likely peaked. Depletion of the litter layer and rapid mineralization of nutrients by non-native Asian jumping worms may make ecosystems more susceptible to nutrient losses, and effects may cascade to understory herbs and other soil biota.