Amynthas spp. impacts on seedlings and forest soils are tree species-dependent

Abstract

Asian jumping worms (Amynthas spp.) are recent invaders of Upper Midwest forests. Research has highlighted the impacts of Amynthas earthworms on soil biogeochemistry and structure, and field observations suggest that Amynthas spp. decrease litter horizon depth and alter plant communities. However, the extent to which Amynthas spp. effects vary among forest types and with worm density and the mechanisms driving these effects are unknown. We conducted a 3-month tree seedling study to evaluate the effects of Amynthas spp. on tree seedling growth and a mesocosm field experiment to evaluate Amynthas spp. effects on soil carbon and nutrient cycling, soil structure, and leaf litter decomposition rates across forest types. In the seedling study, Amynthas spp. enhanced the growth of sugar maple and European buckthorn seedlings and decreased the growth of white oak seedlings. These effects were due to Amynthas spp.-induced changes in soil properties. In the mesocosm study, as Amynthas spp. density increased, carbon mineralization and carbon, nitrogen, and phosphorus availability increased in white oak forest soils and decreased in sugar maple forest soils, while decomposition rates of European buckthorn litter increased as Amynthas spp. density increased. Amynthas spp. altered soil structure similarly across all forest soil types. Taken together, our results suggest that Amynthas spp. have the potential to alter forest ecosystem dynamics via feedbacks among tree species, seedlings, and soil biogeochemistry. However, Amynthas spp. effects on tree seedlings and forest soils are largely context-dependent, and the direction and magnitude of these effects are mediated by tree species.