Consumption of atmospheric methane by the Qinghai–Tibetan Plateau alpine steppe ecosystem

Methane (CH4) cycle on the Qinghai–Tibetan Plateau (QTP), the world's largest high-elevation permafrost region, is sensitive to climate change and subsequent cryoturbation dynamics. Yet its magnitudes, patterns, and environmental controls are still poorly understood. Here we report results from five continuous year-round CH4 observation from a typical alpine steppe ecosystem in the QTP permafrost region. Results suggested the QTP permafrost region was a CH4 sink of −0.86 ± 0.23 g CH4–C m-2 yr1 over 2012–2016, a rate higher than that of many other permafrost areas such as Arctic tundra in northern Greenland, Alaska, and western Siberia. Soil temperature and soil water content were dominant factors controlling CH4 fluxes and their correlations however changed with soil depths due to cryoturbation dynamics. This region was a net CH4 sink in autumn, but a net source in spring, despite both seasons experienced similar top soil thawing and freeze dynamics. The opposite effect was likely caused by their season–specialized cryoturbation processes, which modified the vertical distribution of soil layers that are highly mixed like a multi–layer hamburger in autumn, but not in spring. Furthermore, the traditional definition of four seasons failed to capture the pattern of annual CH4 cycle. We developed a new season division method based on soil temperature, bacteria activities, and permafrost active layer thickness, which significantly improved the modelling of annual CH4 cycle. Collectively, our findings highlight the critical role of fine–scale climate and cryoturbation in driving permafrost CH4 dynamics, which needs to be better monitored and modelled in Earth system models.