Abstract
High-latitude and high-altitude regions contain vast stores of permafrost carbon. Climate warming may result in the release of CO(2) from both the thawing of permafrost and accelerated autotrophic respiration, but it may also increase the fixation of CO(2) by plants, which could relieve or even offset the CO(2) losses. The Tibetan Plateau contains the largest area of alpine permafrost on Earth. However, the current status of the net CO(2) balance and feedbacks to warming remain unclear, given that the region has recently experienced an atmospheric warming rate of over 0.3 °C decade(-1) We examined 32 eddy covariance sites and found an unexpected net CO(2) sink during 2002 to 2020 (26 of the sites yielded a net CO(2) sink) that was four times the amount previously estimated. The CO(2) sink peaked at an altitude of roughly 4,000 m, with the sink at lower and higher altitudes limited by a low carbon use efficiency and a cold, dry climate, respectively. The fixation of CO(2) in summer is more dependent on temperature than the loss of CO(2) than it is in the winter months, especially at higher altitudes. Consistently, 16 manipulative experiments and 18 model simulations showed that the fixation of CO(2) by plants will outpace the loss of CO(2) under a wetting-warming climate until the 2090s (178 to 318 Tg C y(-1)). We therefore suggest that there is a plant-dominated negative feedback to climate warming on the Tibetan Plateau.