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Simulated chronic nitrogen deposition increases carbon storage in Northern Temperate forests

Authors

  • KURT S. PREGITZER,

    1. Ecosystem Science Center, School of Forest Resources & Environmental Science, Michigan Technological University, Houghton, MI 49931, USA,
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    • 1Present Address: Department of Natural Resources and Environmental Science, University of Nevada, Reno, NV 89512, USA.

  • ANDREW J. BURTON,

    1. Ecosystem Science Center, School of Forest Resources & Environmental Science, Michigan Technological University, Houghton, MI 49931, USA,
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  • DONALD R. ZAK,

    1. School of Natural Resources & Environment, University of Michigan, Ann Arbor, MI 48109, USA,
    2. Department of Ecology & Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA
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  • ALAN F. TALHELM

    1. Ecosystem Science Center, School of Forest Resources & Environmental Science, Michigan Technological University, Houghton, MI 49931, USA,
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Kurt S. Pregitzer, tel. +1 775 784 4000, fax +1 775 784 4583, e-mail: ksp@cabnr.unr.edu

Abstract

High levels of atmospheric nitrogen (N) deposition in Europe and North America were maintained throughout the 1990s, and global N deposition is expected to increase by a factor of 2.5 over the next century. Available soil N limits primary production in many terrestrial ecosystems, and some computer simulation models have predicted that increasing atmospheric N deposition may result in greater terrestrial carbon (C) storage in woody biomass. However, empirical evidence demonstrating widespread increases in woody biomass C storage due to atmospheric N deposition is uncommon. Increased C storage in soil organic matter due to chronic N inputs has rarely been reported and is often not considered in computer simulation models of N deposition effects. Since 1994, we have experimentally simulated chronic N deposition by adding 3 g N m−2 yr−1 to four different northern hardwood forests, which span a 500 km geographic gradient in Michigan. Each year we measured tree growth. In 2004, we also examined soil C content to a depth of 70 cm. When we compared the control treatment with the NO3 deposition treatment after a decade of experimentation, ecosystem C storage had significantly increased in both woody biomass (500 g C m−2) and surface soil (0–10 cm) organic matter (690 g C m−2). The increase in surface soil C storage was apparently driven by altered rates of organic matter decomposition, rather than an increase in detrital inputs to soil. Our results, for study locations stretching across hundreds of kilometers, support the hypothesis that chronic N deposition may increase C storage in northern forests, potentially contributing to a sink for anthropogenic CO2 in the northern Hemisphere.

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