Potential and actual trace gas fluxes in Arctic terrestrial ecosystems

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Abstract
This paper provides an overview of results obtained through a number of studies of actual and potential trace gas exchanges in Eurasian and Greenlandic tundra ecosystems. The chief findings include: i) Long-term accumulation rates of carbon in organic tundra soils, i.e. net uptake of atmospheric CO2, are strongly controlled by simple climatic parameters (mean July temperature, annual precipitation). Warmer and wetter conditions stimulate carbon sequestration rates in Arctic terrestrial ecosystems. ii) The release of carbon through ecosystem respiration is also heavily influenced by climate. However, the release of dead organic soil carbon as CO2 is constraind by the lability of the stored organic compounds. This lability decreases significantly with depth (i.e. age) of the soils; moreover, this in turn decreases the temperature sensitivity of the decomposition process. iii) Methane emissions from typical tundra habitats in northern Eurasia are slightly lower than from seemingly similar habitats in North America although this difference probably can be attributed to the colder climatic setting of the studied sites compared with the general climatic conditions at the North American sites. There is a strong linkage between CO2 exchange, CH4 formation and emission rates in some wet tundra ecosystems. iv) Atmospheric uptake of CH4 occurs in some dry and mesic tundra habitats and there are indications that these uptake rates could be affected negatively by atmospheric nitrogen deposition. Emissions of N2O are rarely seen fromArctic soils but there appear to be a strong potential for denitrification and, hence, N2O release. This might be due to high rates of denitrification during the spring thaw and possibly associated significant releases of N2O in this period.