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.