High arctic heath soil respiration and biogeochemical dynamics during summer and autumn freeze-in – effects of long-term enhanced water and nutrient supply

Authors

  • Casper T. Christiansen,

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    • Physiological Ecology Group, Terrestrial Ecology Section, Department of Biology, University of Copenhagen, Copenhagen Ø, Denmark
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  • Sarah H. Svendsen,

    1. Physiological Ecology Group, Terrestrial Ecology Section, Department of Biology, University of Copenhagen, Copenhagen Ø, Denmark
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  • Niels M. Schmidt,

    1. Department of Bioscience, Aarhus University, Roskilde, Denmark
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  • Anders Michelsen

    1. Physiological Ecology Group, Terrestrial Ecology Section, Department of Biology, University of Copenhagen, Copenhagen Ø, Denmark
    2. Center for Permafrost, University of Copenhagen, Copenhagen K, Denmark
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Correspondence: Casper T. Christiansen, Department of Biology, Queen's University, Biosciences Complex, 116 Barrie Street, Kingston ON K7L 3N6, Canada, e-mail: christiansen.c@queensu.ca

Abstract

In High Arctic NE Greenland, temperature and precipitation are predicted to increase during this century, however, relatively little information is available on the role of increased water supply on soil CO 2 efflux in dry, high arctic ecosystems. We measured soil respiration (Rsoil) in summer and autumn of 2009 in combination with microbial biomass and nutrient availability during autumn freeze-in at a dry, open heath in Zackenberg, NE Greenland. This tundra site has been subject to fully factorial manipulation consisting of increased soil water supply for 14 years, and occasional nitrogen (N) addition in pulses. Summer watering enhanced Rsoil during summer, but decreased Rsoil in the following autumn. We speculate that this is due to intensified depletion of recently fixed plant carbon by soil organisms. Hence, autumn soil microbial activity seems tightly linked to growing season plant production through plant-associated carbon pools. Nitrogen addition alone consistently increased Rsoil, but when water and nitrogen were added in combination, autumn Rsoil declined similarly to when water was added alone. Despite several freeze-thaw events, the microbial biomass carbon (C) remained constant until finally being reduced by ~60% in late September. In spite of significantly reduced microbial biomass C and phosphorus (P), microbial N did not change. This suggests N released from dead microbes was quickly assimilated by surviving microbes. We observed no change in soil organic matter content after 14 years of environmental manipulations, suggesting high ecosystem resistance to environmental changes.

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