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Significance of cold-season respiration and photosynthesis in a subarctic heath ecosystem in Northern Sweden

Authors

  • KLAUS STEENBERG LARSEN,

    1. Department of Terrestrial Ecology, Institute of Biology, University of Copenhagen, Oester Farimagsgade 2D, DK-1353 Copenhagen K, Denmark,
    2. Risoe National Laboratory, Biosystems Department, Building BIO-309, PO Box 49, Frederiksborgvej 399, DK-4000 Roskilde, Denmark
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  • ANDREAS IBROM,

    1. Risoe National Laboratory, Biosystems Department, Building BIO-309, PO Box 49, Frederiksborgvej 399, DK-4000 Roskilde, Denmark
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  • SVEN JONASSON,

    1. Department of Terrestrial Ecology, Institute of Biology, University of Copenhagen, Oester Farimagsgade 2D, DK-1353 Copenhagen K, Denmark,
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  • ANDERS MICHELSEN,

    1. Department of Terrestrial Ecology, Institute of Biology, University of Copenhagen, Oester Farimagsgade 2D, DK-1353 Copenhagen K, Denmark,
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  • CLAUS BEIER

    1. Risoe National Laboratory, Biosystems Department, Building BIO-309, PO Box 49, Frederiksborgvej 399, DK-4000 Roskilde, Denmark
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Klaus Steenberg Larsen, Risoe National Laboratory, Biosystems Department, Building BIO-309, PO Box 49, Frederiksborgvej 399, DK-4000 Roskilde, Denmark, fax +45 4677 4160, e-mail: klaus.steenberg.larsen@risoe.dk

Abstract

While substantial cold-season respiration has been documented in most arctic and alpine ecosystems in recent years, the significance of cold-season photosynthesis in these biomes is still believed to be small. In a mesic, subartic heath during both the cold and warm season, we measured in situ ecosystem respiration and photosynthesis with a chamber technique at ambient conditions and at artificially increased frequency of freeze–thaw (FT) cycles during fall and spring. We fitted the measured ecosystem exchange rates to respiration and photosynthesis models with R2-values ranging from 0.81 to 0.85. As expected, estimated cold-season (October, November, April and May) respiration was significant and accounted for at least 22% of the annual respiratory CO2 flux. More surprisingly, estimated photosynthesis during this period accounted for up to 19% of the annual gross CO2 uptake, suggesting that cold-season photosynthesis partly balanced the cold-season respiratory carbon losses and can be significant for the annual cycle of carbon. Still, during the full year the ecosystem was a significant net source of 120 ± 12 g C m−2 to the atmosphere. Neither respiration nor photosynthetic rates were much affected by the extra FT cycles, although the mean rate of net ecosystem loss decreased slightly, but significantly, in May. The results suggest only a small response of net carbon fluxes to increased frequency of FT cycles in this ecosystem.

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