Climate Warming and Soil Drying Significantly Enhance the Methane Uptake in China's Grasslands

Grassland ecosystems are among the largest biogenic methane sinks and play a vital role in the global methane budgets. However, current assessments of methane uptake by grasslands remain uncertain due to limited observational data and unclear driving mechanisms. In this study, we compiled 1229 field measurements from 129 sampling sites across diverse grassland types in China and employed a Random Forest model to study the spatiotemporal dynamics and environmental drivers of methane uptake flux from 1982 to 2020. The results showed that the average methane uptake flux was estimated at 44.4 μg CH₄ m^-2 h^-1. Spatially, higher uptake rates were observed in the southern and eastern regions of the Inner Mongolian Plateau and Junggar Basin, while relatively lower rates occurred in the eastern Qinghai-Tibet Plateau. Temporally, the methane uptake in grasslands in China increased significantly over the 38-year study period, with shrubland and meadow grasslands contributing most to this trend. Further analysis identified rising temperatures and soil drying as the dominant drivers of the observed increase in methane uptake flux. This study provides a spatiotemporal dataset of methane fluxes in China's grassland ecosystem and offers theoretical support for understanding global methane budget changes and the underlying driving mechanisms under climate warming.