Plant uptake of CO2 outpaces losses from permafrost and plant respiration on the Tibetan Plateau
Cold regions contain vast stores of permafrost carbon. Rapid warming will cause permafrost to thaw and plant respiration to accelerate, with a resultant loss of CO2, but could also increase the fixation of CO2 by plants. A network of 32 eddy covariance sites on the Tibetan Plateau, which has the largest store of alpine permafrost carbon on Earth, shows that this region functions as a net CO2 sink. Our sensitivity analyses, experiments, and model simulations consistently showed that the fixation of CO2 by plants outpaces the loss of CO2 from permafrost and accelerates plant respiration. This indicates a plant-dominated CO2 balance on the Tibetan Plateau, which could provide a negative feedback to climate warming.
High-latitude and high-altitude regions contain vast stores of permafrost carbon. Climate warming may result in the release of CO2 from both the thawing of permafrost and accelerated autotrophic respiration, but it may also increase the fixation of CO2 by plants, which could relieve or even offset the CO2 losses. The Tibetan Plateau contains the largest area of alpine permafrost on Earth. However, the current status of the net CO2 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 CO2 sink during 2002 to 2020 (26 of the sites yielded a net CO2 sink) that was four times the amount previously estimated. The CO2 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 CO2 in summer is more dependent on temperature than the loss of CO2 than it is in the winter months, especially at higher altitudes. Consistently, 16 manipulative experiments and 18 model simulations showed that the fixation of CO2 by plants will outpace the loss of CO2 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.
The full article is available on the PNAS website at https://www.pnas.org/content/118/33/e2015283118]]>