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The Effect of Elevated CO2 on N2O and CH4 Fluxes from a Warming and Drying Temperate Heathland
Reference
Carter, M.S., Ambus, P., Albert, K.R., Larsen, K.S., Andersson, M., Prieme, A. van der Linden, L. and Beier, C. 2011. Effects of elevated atmospheric CO2, prolonged summer drought and temperature increase on N2O and CH4 fluxes in a temperate heathland. Soil Biology & Biochemistry 43: 1660-1670.

Background
The authors write that "in temperate regions, climate change is predicted to increase annual mean temperature and intensify the duration and frequency of summer droughts, which together with elevated atmospheric carbon dioxide concentrations, may affect the exchange of nitrous oxide (N2O) and methane (CH4) between terrestrial ecosystems and the atmosphere."

What was done
Working in a dry temperate heathland with a nutrient-poor sandy soil located about 50 km northwest of Copenhagen, Denmark -- the vegetation of which was dominated by Scotch Heather (Calluna vulgaris), Wavy Hairgrass (Deschampsia flexuosa) and various mosses -- Carter et al. investigated "the effects of future climatic and atmospheric conditions on the biosphere-atmosphere exchange of N2O and CH4," which are important greenhouse gases in their own right.

What was learned
The eight Danish researchers report that warming by itself increased CH4 uptake by about 20%, while "elevated concentrations of atmosphericCO2 had no overall effect on the CH4 flux, but reduced the CH4 uptake during one measuring campaign in the winter season." And they say that "in combination, the stimulating effect of warming and the episodic reducing effect of CO2 on the CH4 uptake resulted in a modest, but insignificant, increase in the CH4 uptake when comparing the multifactor treatment including elevated CO2, warming and summer drought with the ambient treatment."

With respect to N2O, the researchers write that "as single experimental factors, elevated CO2, temperature and summer drought had no major effect on the N2O fluxes, but the combination of CO2 and warming stimulated N2O emission, whereas the N2O emission ceased when CO2 was combined with drought."

What it means
As a result of their observations, Carter et al. say that their study "highlights the importance of evaluating climate change parameters in multifactor treatments as the response of CH4 and N2O flux rates to different two- and three-factor combinations may not be predicted from the responses to the individual treatments." And they state that "overall, our study suggests that in the future, CH4 uptake may increase slightly, while N2O emission will remain unchanged in temperate ecosystems on well-aerated soils."

Reviewed 17 August 2011