The transient shift of driving environmental factors of carbon dioxide and methane fluxes in Tibetan peatlands before and after hydrological restoration

Peatlands on the Tibetan Plateau play crucial roles in regional carbon cycling but faced serious degradation in recent decades, and hydrological restoration is being conducted to regain their ecosystem function. However, how restoration affects the environmental controls on carbon processes of these unique ecosystems remains unclear, and the role of vegetation community in regulating carbon processes in response to the restoration is unknown. A long dam was built at the outlet of a large shallow lake on the plateau in order to evaluate the effects of hydrological restoration on the carbon sequestration of the world's largest alpine peatlands. The carbon dioxide (CO2) and methane (CH4) fluxes from three widely distributed peatland communities, i.e., Kobresia pusilla, Carex enervis, and Carex muliensis commuities, were investigated immediately before and after restoration. The water table rising as a consequence of restoration, at least temporarily, decreased the carbon consumption rate (plant respiration plus soil decomposition) for each unit of carbon fixation by plants, which is community dependent. However, a positive relationship between temperature sensitivity of ecosystem respiration (Reco) and optimal water table for respiration implies a positive feedback between water table rising and warming on Reco. Meanwhile, the dominant factor explaining the variance of Reco shifted from soil temperature (explained 56%) to water table (explained 68%) after restoration. Water table rising enhanced the CH4 emissions by 3-12 times, with significantly different changes in CH4 flux over a standard variation in water table level among the communities. Temperature was excluded while only water table and vegetation type were included in the model to predict CH4 fluxes after restoration in contrast to before. We argue that the shift of driving environmental factors and the role of vegetation community are essential in evaluating the effects of hydrological restoration on carbon cycling of Plateau peatlands, particularly during the transitional period.