Increased plant growth may offset soil carbon loss caused by warming in an alpine Sibiraea angustata shrub ecosystem on the eastern Qinghai-Tibet Plateau

Abstract

The alpine shrub ecosystem on the Qinghai-Tibet Plateau, which reserves large amounts of carbon (C) and functions as an important potential C sink, is experiencing significant warming. However, we still lack a thorough understanding of the effects of warming on ecosystem C storage and allocation in above- and belowground components of plants and soils in these alpine shrub ecosystems. In this study, we employed a four-year field warming experiment in an alpine shrubland dominated by Sibiraea angustata on the eastern Qinghai-Tibetan Plateau. We investigated the effects of warming on C storage and allocation among the above- (i.e., leaf and stem) and belowground parts (i.e., coarse and fine roots) of shrubs and the above- and belowground parts of grasses and soils. Our results showed that warming significantly increased shrub leaf C storage by 18.8%, but shrub stem C storage did not respond to warming. Warming significantly increased the C storage of shrub coarse and fine roots by 7.7% and 139.4%, respectively. Warming significantly increased the C storage of the above- and belowground parts of grasses by 60.4% and 130.5%, respectively. As a result, warming significantly increased the C storage of both the above- and belowground parts of total plants by 8.8% and 49.1%, respectively. Moreover, warming significantly increased the C root:shoot ratios of alpine shrubs and grasses. Taken together, warming significantly increased the C storage of total plants by 1.23 kg C m−2, which primarily resulted from the belowground parts of plants (1.07 kg C m−2), and warming-induced increases in C storage of alpine shrub fine roots (0.86 kg C m−2) could approximately offset soil C losses (0.99 kg C m−2), as indicated by decreasing soil C storage under warming. Therefore, warming increased the ecosystem C sink by 0.24 kg C m−2. Our results highlight that alpine shrub fine roots play a dominant role in regulating the dynamics of ecosystem C balance and cycling in response to warming. Future climate warming will stimulate ecosystem C sequestration, largely because of increasing the growth of alpine shrub fine roots in these alpine shrublands on the Qinghai-Tibet Plateau.