Temporal-spatial characteristics and environmental controls of annual CH$_4$ fluxes in a Tibetan alpine landscape

Alpine ecosystems on the Tibetan Plateau are characterized by different soil hydrothermal conditions and vegetation composition across the elevation gradient, and contribute differently to the net landscape methane (CH4) budget. However, the spatiotemporal variation of CH$_4$ fluxes from alpine ecosystems remains poorly understood, underpinning the uncertainty of upscaling the regional and global CH$_4$ budgets. Here, we investigated the spatial and temporal patterns and environmental controls of CH$_4$ fluxes over two years across a Tibetan alpine landscape spanning different elevations (spanning 3200-3500 m above sea level) and major ecosystem types (including alpine meadow, steppe, forest and wetland). On the annual scale, all alpine upland (meadow, steppe and forest) ecosystems consistently functioned as soil CH$_4$ sinks, ranging between 1.12 and 2.49 kg C ha$^{-1}$ yr$^{-1}$, whereas alpine wetlands emitted 17.2-34.3 kg C ha$^{-1}$ yr$^{-1}$ to the atmosphere. Non-growing season CH$_4$ fluxes accounted for 29-46 % of the annual budgets, underscoring its significant contribution that was often neglected in previous studies. Our study also demonstrated that for individual alpine upland and wetland ecosystems, soil water content and soil temperature were the main factors regulating the seasonal patterns of CH$_4$ fluxes. ... mehrWhile across all alpine ecosystems, soil water content outweighed temperature as the primary control on the landscape patterns of CH$_4$ fluxes and higher wetland CH$_4$ emissions were associated with increased soil inorganic N availability. Despite their small area contribution to the landscape, alpine wetlands emitted disproportionate amounts of CH$_4$, weakening the landscape CH$_4$ sink. The resulting net landscape CH$_4$ balance was a weak sink of 0.72 kg C ha$^{-1}$ yr$^{-1}$. Overall, the multiple parameters and insights gained from our study provide valuable information for better predicting the role of alpine ecosystem CH$_4$ carbon-climate feedbacks in high-altitude regions.