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Increased CO2 efflux due to long-term experimental summer warming and litter input in subarctic tundra – CO2 fluxes at snowmelt, in growing season, fall and winter



Soils of northern latitude tundra ecosystems have accumulated large amounts of carbon that might be released as CO2 when temperature rises and the tree-line moves north. We aim to investigate the potential CO2 flux changes at a subarctic tundra heath under changing climate.


We measured daytime ecosystem respiration and photosynthesis at a subarctic heath over a full year under ambient conditions and in factorial long-term (13 years) increased summer temperature and leaf litter addition plots, and in additional short-term (2 years) summer warming plots.


Under ambient conditions the ecosystem was a daytime sink of CO2 in the five warmest months, but a net daytime source in the cold season. Thirteen years of summer warming by 1 °C at soil surface increased CO2 emissions, as daytime respiration increased by 37% and photosynthesis by 29% over the year. Short-term warming likewise increased fluxes. Litter addition also increased the emission of CO2 as ecosystem respiration rose by 21% but photosynthesis remained unchanged. Both warming and litter addition significantly enhanced the amount of green biomass.


This study suggests that in a changed climate subarctic ecosystems will act as a positive feedback source of atmospheric CO2. It shows the significance of CO2 fluxes outside the growing season and demonstrates a cold-season long- but not short-term legacy effect of increased summer warming on CO2 emission.

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We acknowledge The Danish Council for Independent Research and The Danish National Research Foundation (CENPERM DNRF100) for financial support. The research has additionally received funding from INTERACT (grant agreement No 262693) under the European Community’s Seventh Framework Programme. We thank Marie Glahn for field assistance, Abisko Scientific Research Station for logistic support and access to climatic data and Casper T. Christiansen for internal revision of the manuscript.

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Correspondence to Anders Michelsen.

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Finderup Nielsen, T., Ravn, N.R. & Michelsen, A. Increased CO2 efflux due to long-term experimental summer warming and litter input in subarctic tundra – CO2 fluxes at snowmelt, in growing season, fall and winter. Plant Soil 444, 365–382 (2019).

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  • Carbon dioxide fluxes
  • Climate change
  • NDVI
  • Net ecosystem production
  • Photosynthesis
  • Respiration