CO2, CH4 and N2O fluxes in an alpine meadow on the Tibetan Plateau as affected by N-addition and grazing exclusion

Limited understanding of the effects of enhanced nitrogen (N) addition and grazing exclusion (E) on greenhouse gases fluxes (GHGs: CO2, CH4, and N2O) in grasslands constrains our ability to respond to the challenges of future climate change. In this study, we conducted a field experiment using a static closed opaque chamber to investigate the response of GHG fluxes to N addition (69 kg N ha(-1) year(-1) applied in 3 splits) and grazing exclusion in an alpine meadow on the Tibetan Plateau during the growing seasons from 2011 to 2013. Our results showed that winter grazing significantly raised soil temperature (ST), while grazing exclusion (E) had no effect on soil moisture (SM), and N fertilizer (F) had no effect on ST or SM. Aboveground biomass (AB) and root biomass (RB) were not significantly affected by E in 2011-2013 (p > 0.05), but F significantly affected AB and RB (p < 0.05). Compared with winter grazing, only E substantially reduced seasonal mean CO2 emissions (by about 20.1%) during the experimental period. E did not significantly directly affect CH4 uptake, whereas N addition reduced seasonal mean CH4 uptake by about 6.5%, and N addition changed seasonal average absorption of N2O into an emission source. CO2 flux is the major contributor to CO2 equivalent emissions in this area. Our results indicate that exclosure from livestock grazing might be a promising measure to reduce CO2 emissions, while enhanced N addition might reduce CH4 uptake and increase N2O emission in the alpine meadow under future climate change.