Convergent control of soil temperature on seasonal carbon flux in Tibetan alpine meadows: An in-situ monitoring study

The Tibet Plateau, with its extensive carbon pools, plays a pivotal role in the global carbon budget. Nevertheless, the driving factors of the carbon dioxide budget remain disputed, and the impact of freeze-thaw process on carbon release is still unclear due to the harsh climate and lack of monitoring data. To clarify the primary factors affecting the alpine meadow ecosystems and to examine the impact of freeze-thaw on carbon release, we employed the LI-8150 automated continuous measurement system. This system, in conjunction with eddy covariance meteorological data, The Boosted Regression Tree (BRT) model, and multiple stepwise regression analysis, were used to analyze the seasonal variations in carbon flux (e.g., net ecosystem carbon exchange [NEE], gross primary productivity [GPP], and ecosystem respiration [R-eco]). We also investigate the carbon sources and sinks in the alpine meadow ecosystem, as well as the predominant factor of carbon flux. Our findings include: (1) the carbon sources and sinks in the alpine meadow ecosystem shift seasonally on monthly and daily scales. On a monthly scale, the ecosystem functions as a moderate carbon sink in June, July, August, and September and as a weak carbon source from October through May. (2) Overall, the alpine meadow ecosystem, located in the northeastern Qinghai Lake basin, serves as a weak carbon sink (-58.53 g C m(-2) year(-1)). (3) Soil temperature is the primary factor driving most variations observed in NEE, Reco, and GPP, contributing 48.05 %, 78.61 %, and 65.05 %, respectively. Soil temperature, soil water dynamics influenced by freeze and thaw processes, and their interaction with plant growth collectively play a crucial role in regulating the carbon sources and sinks in ecosystems. We provide first-hand observational data for monitoring the carbon sources and sinks in the alpine meadow ecosystem of the Tibet Plateau, as well as offer future guidance for studying the carbon budget of the Tibet Plateau.