Spring factors controlling interannual CO2 flux variations in a subtropical humid alpine meadow on the southeastern Tibetan Plateau

Understanding of the carbon cycling in subtropical humid alpine meadows is still limited due to the scarcity of observations in this area. It is crucial to quantify the temporal dynamics and factors influencing CO₂ fluxes in order to predict ecosystems CO₂ budgets accurately under climate change. This study utilized 11 years (2012–2022) of eddy covariance observation data to investigate CO₂ fluxes and its controlling factors in a subtropical humid alpine meadow on the southeastern Tibetan Plateau. Our findings indicate that this alpine meadow ecosystem consistently acted as a net CO₂ sink, with annual net ecosystem productivity (NEP) ranging from 137 g C m⁻² to 370 g C m⁻². Seasonal variations in CO₂ fluxes were primarily governed by soil water content, soil temperature (Ts), and leaf area index, with notable interactions observed among these variables. On an annual basis, the interannual variability (IAV) of NEP anomalies was predominantly linked to gross primary production (GPP) anomalies during the dry season. IAV of NEP was mainly driven by length of growing season, while that of GPP and ecosystem respiration were significantly affected by summer peak values. Additionally, spring environmental variables, i.e., Ts, vapor pressure deficit, and photosynthetically active radiation, were crucial in influencing the IAV of CO₂ fluxes through the regulation of phenological and physiological metrics. This comprehensive analysis provides valuable insights for future carbon modeling efforts on the Tibetan Plateau.