摘要：The greenhouse gas sources-sink functions of temperate semiarid steppes may be changing due to rangeland overgrazing and climate change. However, the comprehensive effects of grazing patterns and environmental factors on soil carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) exchanges have been poorly studied. Using soil core incubation and gas chromatography methods, we determined the potential of CO2, CH4 and N2O fluxes of steppe topsoil that sampled from various grazing intensities (i.e., ungrazed, lightly-grazed, moderately-grazed and heavily-grazed)under combined conditions with air temperatures (i.e., 5 °C and 20 °C) and soil moistures (i.e., 5%, 12.5%, 20% and 30% v/v) at two dominant vegetation types (i.e., Stipa grandis and Leymus chinensis).Both steppe soils were a sink of CH4 (-37.9 ± 5.8 pg C m-2 h-1) and sources of N2O (9.9 ± 4.6 pg N m-2 h-1) and CO2 (65.4 ± 7.7 mg C m-2 h-1), respectively. The Leymus chinensis steppe showed higher potential of CH4 sink, CO2 and N20 sources as compared toStipa grandis steppe. Lower temperature (5 °C) and higher soil moisture (30%) significantly inhibited CH4 uptake, and both lower temperature (5 °C) and soil moisture (5%) significantly decreased soil respirations (i.e., CO2 flux) and N2O emissions. The ungrazed steppes absorbed CH4, emitted CO2 and N2O, with average fluxes of -46.8 ± 5.2 pg C m-2 h-1, 82.7 ± 22.1 mg C m-2 h-1 and 10.7 ± 3.5 pg N m-2 h-1, respectively. Heavy grazing significantly reduced CH4 uptake by 43% and soil respiration by 42%, but did not significantly affect N2O emissions. The relationships between stoking rates and CH4 uptake and N2O emissions indicate light and moderate grazing could be benefit to improve soil sink and source functions of CH4 and reduce N2O emission during the growing season.
