Effects of Climate Change Drivers on Nitrous Oxide Fluxes in an Upland Temperate Grassland

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 (N2O) fluxes. The aim of this study was to determine the importance of the three main drivers of climate change (warming, summer drought, and elevated CO2 concentrations) on N2O fluxes from an extensively managed, upland grassland. Over a 2-year period, we monitored N2O fluxes in an in situ ecosystem manipulation experiment simulating the climate predicted for the study area in 2080 (3.5C temperature increase, 20 % reduction in summer rainfall and atmospheric CO2 levels of 600 ppm). N2O fluxes showed sig-nificant seasonal and interannual variation irre-spective of climate treatment, and were higher in summer and autumn compared with winter and spring. Overall, N2O emissions showed a positive correlation with soil temperature and rainfall. Ele-vated temperature had a positive impact on mean annual N2O fluxes but effects were only significant in 2007. Contrary to expectations, neither com-bined summer drought and warming nor the simultaneous application of elevated atmospheric CO2 concentrations, summer drought and warming had any significant effect on annual N2O fluxes. However, the maximum N2O flux rates observed during the study occurred when elevated CO2 was combined with warming and drought, suggesting the potential for important, short-term N2O–N losses in enriched CO2 environments. Taken to-gether, our results suggest that the N2O responses of temperate, extensively managed grasslands to future climate change scenarios may be primarily driven by temperature effects. Key words: drought; elevated CO2; grasslands; interannual variation; nitrous oxide emission; warming