干旱区生态环境知识资源中心

Terrestrial ecosystems play a critical role in regulating the emission and uptake of the most important greenhouse gases (GHGs) such as CO2, CH4, and N2O. However, the effects of grazing on these GHG fluxes in different steppe types remain unclear. Here, we compared the effects of grazing on seasonal CO2, CH4, and N2O fluxes in the meadow (MS), typical (TS), and desert (DS) temperate steppe ecosystems in northern China. CO2 emission rates increased from 311.4 +/- 73.2 to 349.6 +/- 55.4 mg.m(-2).h(-1) in MS, but decreased in TS (from 341.3 +/- 93.0 to 239.5 +/- 81.9 mg.m(-2).h(-1)) and DS ( from 212.1 +/- 53.7 to 163.0 +/- 83.4 mg.m(-2).h(-1)) in response to summer grazing (SG). N2O emission rates increased in MS from 4.7 +/- 2.2 to 8.1 +/- 3.4 mu g.m(-2).h(-1), but not significantly changed in TS (9.2 +/- 4.2 vs. 8.4 +/- 2.4 mu g.m(-2).h(-1)) and DS (6.3 +/- 1.5 vs. 5.7 +/- 1.6 mu g.m(-2).h(-1)) by SG. CH4 uptake rates increased in MS from 33.0 +/- 11.7 to 47.1 +/- 10.4 mu g.m(-2).h(-1) and decreased from 64.4 +/- 7.6 to 56.2 +/- 5.9 mu g.m(-2).h(-1) in TS in response to SG. In MS and DS, N2O emissions were positively related to seasonal CO2 emissions and negatively related to CH4 uptakes. No significant relationships were found between GHG fluxes in TS. Summer grazing did not affect the relationship between CO2 and N2O emissions in MS, but reduced the relationship by enhancing the effect of aboveground biomass (AGB) on N2O emission in DS. The significant negative relationship between CH4 uptake and N2O emission in MS and DS could be attributed to the significant relationship between soil temperature (ST) and AGB in MS and to the significant effects of soil moisture on both CH4 uptake and N2O emission in DS. The decrease in the magnitude of the correlation coefficients between CH4 uptake and N2O emission by SG was due to the negative relationship between ST and AGB simultaneously in MS and DS. Our results suggest that effects of SG on GHG fluxes varied in different steppes and the relationship among GHGs was steppe-dependent and SG also changed the relationship by affecting GHG fluxes induced by varied soil and environmental factors.