Influence of exotic earthworm invasion on soil organic matter, microbial biomass and denitrification potential in forest soils of the northeastern United States

Formerly glaciated regions of the northeastern United States have few native earthworm species and the region is dominated by exotic earthworms from Europe and Asia. Earthworms of the Asian Megascolecid genus Amynthas, common in many forests of the southeastern US, are invading new habitats in north of their reported range in the northeastern US. At the Cary Arboretum in Millbrook, NY (approximately 42 degrees N latitude, 74 degrees W longitude), we discovered distinct patches of forest soil invaded by Amynthas hawayanus which were adjacent to areas of forest soil with no earthworms. We sampled soil within and just outside of the worm patches to assess the influence of earthworm invasion on the following soil chemical and biological characteristics: soil NO3- and NH4+ concentrations, microbial biomass carbon (C) and nitrogen (N), readily-mineralizable C, organic matter content, pH and denitrification enzyme activity (DEA). Soil patches with earthworms had greatly increased fractions of active and readily-mineralizable soil organic matter compared with patches lacking worms. Readily-mineralizable and microbial biomass C, expressed per gram of soil organic matter, were 1.4-fold greater within the worm patches than outside the patches. Microbial biomass N per gram of organic matter was 2.4-fold greater, and DEA was 2.7-fold greater, in the worm patches than in surrounding soil. Earthworms apparently decreased the organic matter content of the O horizon by 36%. Our results strongly suggest that invasion of forests in the northeastern US by these exotic earthworms increases both C and N flux, with potentially important long-term consequences for nutrient cycling in these ecosystems. (C) 1998 Elsevier Science B.V.