Effects of Climate Change Drivers on Nitrous Oxide Fluxes in an Upland Temperate Grassland
Résumé
Despite increasing interest in the patterns of trace gas emissions in terrestrial ecosystems, little is known about the impacts of climate change on nitrous oxide (N(2)O) fluxes. The aim of this study was to determine the importance of the three main drivers of climate change (warming, summer drought, and elevated CO(2) concentrations) on N(2)O fluxes from an extensively managed, upland grassland. Over a 2-year period, we monitored N(2)O fluxes in an in situ ecosystem manipulation experiment simulating the climate predicted for the study area in 2080 (3.5A degrees C temperature increase, 20% reduction in summer rainfall and atmospheric CO(2) levels of 600 ppm). N(2)O fluxes showed significant seasonal and interannual variation irrespective of climate treatment, and were higher in summer and autumn compared with winter and spring. Overall, N(2)O emissions showed a positive correlation with soil temperature and rainfall. Elevated temperature had a positive impact on mean annual N(2)O fluxes but effects were only significant in 2007. Contrary to expectations, neither combined summer drought and warming nor the simultaneous application of elevated atmospheric CO(2) concentrations, summer drought and warming had any significant effect on annual N(2)O fluxes. However, the maximum N(2)O flux rates observed during the study occurred when elevated CO(2) was combined with warming and drought, suggesting the potential for important, short-term N(2)O-N losses in enriched CO(2) environments. Taken together, our results suggest that the N(2)O responses of temperate, extensively managed grasslands to future climate change scenarios may be primarily driven by temperature effects.