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High nitrogen deposition alters the decomposition of bog plant litter and reduces carbon accumulation

Authors

  • Luca Bragazza,

    Corresponding author
    1. École Polytechnique Fédérale de Lausanne (EPFL), School of Architecture, Civil and Environmental Engineering (ENAC), Laboratory of Ecological Systems (ECOS), Lausanne, Switzerland
    2. Department of Biology and Evolution, University of Ferrara, Ferrara, Italy
    • WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Lausanne, Switzerland
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  • Alexandre Buttler,

    1. WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Lausanne, Switzerland
    2. École Polytechnique Fédérale de Lausanne (EPFL), School of Architecture, Civil and Environmental Engineering (ENAC), Laboratory of Ecological Systems (ECOS), Lausanne, Switzerland
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  • Jonathan Habermacher,

    1. WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Lausanne, Switzerland
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  • Lisa Brancaleoni,

    1. Department of Biology and Evolution, University of Ferrara, Ferrara, Italy
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  • Renato Gerdol,

    1. Department of Biology and Evolution, University of Ferrara, Ferrara, Italy
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  • Hannu Fritze,

    1. Finnish Forest Research Institute, 01301 Vantaa, Finland
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  • Peter Hanajík,

    1. Department of Soil Science, Comenius University, Faculty of Natural Sciences, Bratislava 4, Slovakia
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  • Raija Laiho,

    1. Department of Forest Sciences, University of Helsinki, Peatland Ecology Group, 0014 Helsinki, Finland
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  • David Johnson

    1. University of Aberdeen, Institute of Biological and Environmental Sciences, Aberdeen, UK
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Correspondence: Luca Bragazza, tel. + 39 0532 293773, fax: + 39 0532 293773, e-mail: luca.bragazza@unife.it

Abstract

Bogs are globally important sinks of atmospheric carbon (C) due to the accumulation of partially decomposed litter that forms peat. Because bogs receive their nutrients from the atmosphere, the world-wide increase of nitrogen (N) deposition is expected to affect litter decomposition and, ultimately, the rate of C accumulation. However, the mechanism of such biogeochemical alteration remains unclear and quantification of the effect of N addition on litter accumulation has yet to be done. Here, we show that 7 years of N addition to a bog decreased the C : N ratio, increased the bacterial biomass and stimulated the activity of hydrolytic and oxidative enzymes in surface peat. Furthermore, N addition modified nutrient limitation of microbes during litter decomposition so that phosphorus became a primary limiting nutrient. Alteration of N release from decomposing litter affected bog water chemistry and the competitive balance between peat-forming mosses and vascular plants. We estimate that deposition of about 4 g N m−2 yr−1 will cause a mean annual reduction of fresh litter C accumulation of about 40 g m−2 primarily as a consequence of decreased litter production from peat-forming mosses. Our findings show that N deposition interacts with both above and below ground components of biodiversity to threaten the ability of bogs to act as N-sinks, which may offset the positive effects of N on C accumulation seen in other ecosystems.

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