Effects of warming and clipping on CH4 and N2O fluxes in an alpine meadow

Methane (CH4) and nitrous oxide (N2O) are two greenhouse gases with much more warming potential than carbon dioxide (CO2). However, there have been less studies on their responses to climate warming and land use practices, such as hay harvest in grasslands. Especially, their fluxes are not well estimated during the nongrowing season. In this study, we investigated year-round (August 2015–August 2016) continuous measurements of CH4 and N2O fluxes in response to simulated warming, clipping (as a mimic of hay harvest), and their interaction in an alpine meadow on the Qinghai-Tibetan Plateau. Compared to the control, warming alone and in combination with clipping significantly increased CH4 uptake by 42% and 51%, respectively, on the annual basis. Warming alone also significantly decreased year-round N2O emission by 57% relative to that under control. However, clipping alone did not affect CH4 and N2O fluxes during the study period, and no significant interactive effect of clipping and warming was detected. Furthermore, warming had larger effects on CH4 uptake but smaller effects on N2O emission in the growing than nongrowing season. We also found that the responses in CH4 and N2O fluxes to different treatments were regulated by changes in soil temperature and moisture. Based on sustained global warming potential approach and expressed as CO2-equvalents, the ecosystem switched from a net source of these two gases in the control (1.2 g CO2-eq m-2) to a net sink in warming (-11.3 g CO2-eq m-2) and its combination with clipping (-9.9 g CO2-eq m-2). The findings highlight the importance of understanding greenhouse gas fluxes in the nongrowing season and suggest the increase of CH4 uptake and reduction in N2O emission under climate warming will benefit ecosystem feedback and help mitigate climate change.