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Earthworm abundance and nitrogen mineralization rates along an urban-rural land use gradient
| Author: |
Steinberg, David A.; Pouyat, Richard V.; Parmelee, Robert W.; Groffman, Peter M. |
| Date: |
1997 |
| Periodical: |
Soil Biology and Biochemistry |
| Abstract: |
Preliminary observations of glaciated regions in North America suggest that forest stands associated with urban areas may support high populations of non-native species of earthworms relative to forests in rural areas. Moreover, the presence of these non-native species of worms may be moderating the effects of pollutant deposition on litter quality, or the decomposability of litter, and subsequently nutrient cycling processes in the urban stands. In this study we quantified earthworm abundance and biomass in urban and rural oak forest stands along a 130 x 20 km urban-rural transect in New York City, USA metropolitan area. We also evaluated the effects of earthworms on potential net N mineralization and nitrification in a laboratory microcosm study. Earthworm abundance and biomass along the transect was significantly higher in urban (25.1 individuals m-2 and 2.16 g m-2) than in rural (2.1 individuals m-2 and 0.05 g m-2) stands. In a microcosm study, potential net N mineralization rates (0.15 mg N kg-1 d-I) were significantly higher in urban soil with earthworms than in urban soil without earthworms, which exhibited a net immobilization of N. Rural soil with earthworms had significantly higher rates (0.57 mg N kg-1 d-1) than urban soil with earthworms and rural soil without earthworms (0.28 mg N kg-1 d-1). Nitrification rates in urban soils were surprisingly high given the relatively low litter quality and rates of N mineralization in these soils. The results suggest that earthworms may play an important role in forest ecosystems embedded within urban areas by enhancing nitrogen cycling processes and thereby compensating for the effects of air pollution on litter quality and decomposition. |
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