Moderate grazing has little effect on global warming potential in the temperate steppes of northern China

Abstract

Grazing has been reported to significantly affect the flux of three greenhouse gases (GHGs: CO2, CH4 and N2O) in grasslands, but its effect on total global warming potential (GWP) is still unclear. To assess the effect of grazing on GWP, we simultaneously measured the flux of these three GHGs using static chambers in meadow, typical, and desert steppes under no grazing (NG) and summer grazing (SG) conditions during the 2012-14 growing seasons. We aimed to examine the impact of grazing on total GWP across different steppes and to assess the relative contribution of different environmental factors to changes in GWP. Our results showed that total GWP values were almost entirely negative in all steppe environments and displayed high spatio-temporal variability. Net ecosystem exchange was the most important predictor of total GWP in all three steppes, and the positive GWP induced by N2O emission was approximately equal to the negative GWP induced by CH4 uptake. Steppe type and sampling year—but not grazing treatment—were found to affect GWP. Air temperature and precipitation were the major factors driving total GWP change under the no grazing treatment. In contrast, soil temperature, soil moisture, and precipitation explained a significant percentage of variation in total GWP under the summer grazing treatment. Our study suggests that moderate grazing does not change the role of temperate steppe's function in mitigating climate change; however, multi-year GWP data are necessary for extrapolation to a regional scale.