关键词: 高寒草甸, 高寒湿地, 热浪, 稳定性, 遗留效应, 涡度协方差

Abstract: Over recent decades, the increasing frequency of extreme heat events has led to warmer and drier conditions that significantly impact vegetation productivity and ecosystem carbon sequestration. Based on tower-based flux data (2022-2023) from two contrasting alpine ecosystems (alpine meadow and alpine wetland) on the Qinghai-Xizang Plateau (QXP), we assessed the impact of the 2022 heatwave on carbon fluxes and their underlying mechanisms. The results demonstrated that the heatwave strongly suppressed carbon uptake in the alpine meadow, reducing net ecosystem productivity (NEP), gross primary productivity (GPP), and carbon use efficiency (CUE) by 36.9%, 17.0%, and 14.4%, respectively, while ecosystem respiration (ER) remained unchanged. In contrast, carbon fluxes and CUE in the alpine wetland were largely insensitive to the heatwave, indicating substantially higher thermal resistance. The alpine meadow exhibited post-heatwave legacy effects, with persistent declines in GPP, ER, and NEP, and incomplete recovery of carbon uptake by the end of the growing season. Moreover, the heatwave strengthened soil water content (SWC) as the dominant control on carbon fluxes across both ecosystems. Mechanistically, soil moisture depletion during the heatwave directly constrained GPP and NEP, while elevated VPD further intensified carbon losses through reduced canopy conductance. By contrast, stable soil water availability in the alpine wetland prevented water limitation, enabling higher temperatures to stimulate vegetation growth and carbon uptake. These results highlight the high sensitivity of the QXP alpine carbon sink to climate extremes and the risk of disproportionate productivity losses in water-limited alpine regions under future climate intensification.

Key words: Alpine Meadow, Alpine Wetland, Heatwave, Stability, Legacy impacts, Eddy covariance