Soil nitrogen cycling and nitrous oxide flux in a Rocky Mountain Douglas-fir forest: effects of fertilization,irrigation and carbon addition |
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Authors: | Pamela A Matson Stith Thoma Gower Carol Volkmann Christine Billow Charles C Grier |
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Institution: | (1) Ecosystem Science and Technology Branch, NASA-Ames Research Center, Moffett Field, CA, 94035-1000;(2) Department of Forestry, University of Wisconsin, Madison, WI, 53706;(3) Department of Forest Resources, Utah State University, Logan, UT, 84322-5215 |
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Abstract: | Nitrous oxide fluxes and soil nitrogen transformations were measured in experimentally-treated high elevation Douglas-fir
forests in northwestern New Mexico, USA. On an annual basis, forests that were fertilized with 200 kg N/ha emitted an average
of 0.66 kg/ha of N2O-N, with highest fluxes occurring in July and August when soils were both warm and wet. Control, irrigated, and woodchip
treated plots were not different from each other, and annual average fluxes ranged from 0.03 to 0.23 kg/ha. Annual net nitrogen
mineralization and nitrate production were estimated in soil and forest floor usingin situ incubations; fertilized soil mineralized 277 kg ha−1 y−1 in contrast to 18 kg ha−1 y−1 in control plots. Relative recovery of15NH4-N applied to soil in laboratory incubations was principally in the form of NO3-N in the fertilized soils, while recovery was mostly in microbial biomass-N in the other treatments. Fertilization apparently
added nitrogen that exceeded the heterotrophic microbial demand, resulting in higher rates of nitrate production and higher
nitrous oxide fluxes. Despite the elevated nitrous oxide emission resulting from fertilization, we estimate that global inputs
of nitrogen into forests are not currently contributing significantly to the increasing concentrations of nitrous oxide in
the atmosphere. |
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Keywords: | Douglas-fir forests forest fertlization microbial immobilization in situ incubations N-15 nitrous oxide nitrification nitrogen mineralization |
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