论文摘要：

Soil moisture plays a vital role in regulating the direction and magnitude of methane (CH₄) fluxes. However, it remains unclear whether the responses of CH₄ fluxes to climate warming exhibit difference between dry and moist ecosystems. Based on standardized manipulative experiments (i.e., consistent experimental design and measurement protocols), here we explored warming effects on growing season CH₄ fluxes in two alpine grasslands with contrasting water status on the Tibetan Plateau. We observed that experimental warming enhanced CH₄ uptake in the relatively arid alpine steppe, but had no significant effects on CH₄ emission in the moist swamp meadow. The distinct responses of CH₄ fluxes were associated with the different warming effects on biotic and abiotic factors related to CH₄ oxidation and production processes. Warming decreased soil water-filled pore space (WFPS) and increased the pmoA gene abundance and CH₄ oxidation potential in the alpine steppe, which together led to a significant increase in CH₄ uptake at this alpine steppe site. However, warming-induced enhancement in CH₄ oxidation potential might be counteracted by the simultaneously increased CH₄ production potential in the swamp meadow, which could then result in insignificant warming effects on CH₄ emission at this swamp meadow site. Based on a meta-analysis of warming effects on CH₄ fluxes across the entire Tibetan Plateau, we found that the entire alpine grasslands could absorb an extra 0.042 Tg CH₄ (1 Tg = 10¹² g) per growing season if soil temperature increased by 1 °C. These findings demonstrate that warming effects on CH₄ fluxes differ between two alpine grasslands with contrasting moisture conditions and the entire alpine grasslands may not trigger a positive CH₄ feedback to climate system with moderate warming.