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Appl Environ Microbiol. 1986 December; 52(6): 1287-1292
Copyright © 1986, American Society for Microbiology. All Rights Reserved.

Environmental Parameters Regulating Gaseous Nitrogen Losses from Two Forested Ecosystems via Nitrification and Denitrification

Eric A. Davidson^,* and Wayne T. Swank

² Department of Forestry, North Carolina State University, Raleigh, North Carolina 27695-8002, ¹ and U.S. Department of Agriculture Forest Service Southeastern Experiment Station, Coweeta Hydrologic Laboratory, Otto, North Carolina 28763²

ABSTRACT

Gaseous N losses from disturbed and reference forested watersheds at the Coweeta Hydrologic Laboratory in western North Carolina were studied by in situ N₂O diffusion measurements and laboratory incubations throughout a 10-month period. Soil temperature, percent base saturation, and water-filled pore space accounted for 43% of the variation in in situ N₂O diffusion measurements. Laboratory incubations distinguished the gaseous N products of nitrification and denitrification. Nitrifying activity, ambient NO₃^–, and nitrification N₂O were positively correlated with percent base saturation. However, differences between watersheds in soil N substrate caused by presence of leguminous black locust in the disturbed watershed were confounded with differences in soil acidity. Denitrification was most strongly affected by soil moisture, which in turn was determined by precipitation events and slope position. Gaseous N losses from well-drained midslope and toeslope landscape positions appeared to be minor relative to other N transformations. Favorable conditions for denitrification occurred at a poorly drained site near the stream of the disturbed watershed. Laboratory incubations revealed high rates of NO₃^– reduction in these soils. We speculate that the riparian zone is a major site of depletion of NO₃^– from the soil solution via denitrification.

^* Corresponding author.

Present address: Department of Plant and Soil Biology, University of California, Berkeley, CA 94720.

Paper no. 10424 of the journal series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601.

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