Grazing Stocking Rate and Rainfall Jointly Regulate Soil Methane Uptake in a Temperate Meadow Steppe, but Do Not Reverse Net Methane Emissions.

Grasslands are widely recognized as important sinks of methane (CH4). However, their CH4 uptake capacity has been increasingly weakened driven by human activities and changes in precipitation regimes. In particular, the rapid expansion of livestock grazing can lead to substantial increases in CH4 emissions. For the Eurasian grasslands that have been subject to long-term grazing, how well they currently function and will continue to function as CH4 sinks under the changing precipitation regimes remains uncertain. Here we conducted an 11-year grazing-gradient experiment to assess the combined effects of grazing intensity and precipitation variability on grassland CH4 fluxes. We measured soil CH4 uptake in a manipulative grazing experiment in both wet and dry years, estimated livestock-derived CH4 emissions, and examined a range of biotic and abiotic drivers, including vegetation attributes, soil properties, and microbial biomass, for short- (prior to the onset of the lagged response) and long-term (the entire experimental period) influences on the dynamics of CH4 uptake in temperate meadow grasslands. Over the long term, CH4 fluxes are jointly regulated by precipitation and grazing, with overgrazing amplifying the suppressive effect of rainfall on CH4 uptake. Soil CH4 uptake showed a lagged response to grazing, which may have been triggered by extreme rainfall events. While moderate grazing sustained the long-term CH4 uptake, it fails to offset livestock-derived CH4 emissions. In the short term, CH4 fluxes are primarily governed by grazing, whereas in the long term they are jointly regulated by precipitation and grazing intensity. These results offer a new perspective for understanding the source-sink CH4 dynamics of grasslands in the context of ongoing climate change.