Plant uptake of CO₂outpaces losses from permafrost and plant respiration on the Tibetan Plateau

Abstract

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.

Quantifying net carbon fixation by Tibetan alpine ecosystems should consider multiple anthropogenic activities

“…In PNAS, Wei et al. ( 2 ) present interesting results with combinations of 32 eddy covariance in situ measurements and 16 warming manipulative experiments as well as 18 model simulations across Tibetan alpine ecosystems. They claim that plant uptake of CO 2 outpaces CO 2 losses from permafrost and plant respiration on the Tibetan Plateau and that plants played a dominant role in cooling this plateau under a warming climate.…”

“…In PNAS, Wei et al. ( 2 ) mainly consider the potential influences of ecosystem type, altitude, and permafrost status (continuous or noncontinuous permafrost) but neglect the potential influences of multiple human disturbances on the net ecosystem carbon balance on the Tibetan Plateau. Using the NEP datasets from Wei et al.…”

“…Using the NEP datasets from Wei et al. ( 2 ), we found significantly ( P < 0.001) higher annual NEP for natural alpine peatlands (mean ± 95% confident interval: 1,784 ± 454 kg C⋅ha −1 ⋅y −1 ) than for drained peatlands (–1,180 ± 208 kg C⋅ha −1 ⋅y −1 ) ( Fig. 1 A ), while there were no significant differences in annual NEP between natural and grazed meadows and shrublands ( Fig.…”

Reply to Song and Wang: Terrestrial CO 2 sink dominates net ecosystem carbon balance of the Tibetan Plateau

“…The net ecosystem C balance (NECB) includes CO 2 and CH 4 exchange, volatile organic C loss, and particulate and aquatic C transport. By contrast, our work focused on terrestrial CO 2 exchange ( 2 ), a subset of the NECB. We partly agree with Song and Wang regarding the importance of aquatic C loss, but their conclusion was reached based upon a catchment-scale case study ( 3 ).…”

“…Besides the CO 2 uptake in terrestrial ecosystems ( 2 ), they also regulate the CH 4 exchange. Our observations and simulations ( 8 – 10 ) have characterized alpine grasslands as a considerable CH 4 sink of 0.74 ± 0.06 Tg CH 4 ⋅y −1 , while alpine marshlands emit 0.96 ± 0.21 Tg CH 4 ⋅y −1 .…”