Sensitivity of alpine grassland carbon balance to interannual variability in climate and atmospheric CO2 on the Tibetan Plateau during the last century

As the Earth's third pole, the Tibetan Plateau ecosystems are extremely sensitive to climate change. However, the interannual climate sensitivity of the carbon balance of the Tibetan Plateau alpine grassland has not been well quantified under changes in the climate and atmospheric CO2 concentration. Here, we used a process-based biogeochemistry model, CENTURY, to evaluate the sensitivity of the carbon balance to climate change and rising atmospheric CO2 concentration on the Tibetan Plateau grassland during the period 1901-2010. We show that the magnitude of the increase in net primary production (NPP) (0.31 g C m− 2 yr− 1) was larger than that in heterotrophic respiration (Rh) (0.26 g C m− 2 yr− 1), and thus indicate that the Tibetan Plateau grassland acted as a net carbon sink of 7.45 Tg C yr− 1 from 1901 to 2010. The spatiotemporal dynamics of carbon fluxes in the Tibetan Plateau grassland were primarily controlled by temperature, and positively correlated with precipitation and elevated CO2 concentration. The temperature sensitivities of NPP (γNPPTemp), Rh (γRhTemp), and net ecosystem production (NEP, γNEPTemp) during the period 1961-2010 weakened by 16%, 17%, and 15%, respectively, compared with the period 1901-1960. By contrast, the precipitation sensitivities of these variables, i.e., γNPPPrec, γRhPrec, and γNEPPrec, strengthened by 46%, 67%, and 23%, respectively, from 1961 to 2010 compared with the 1901-1960 period. The continuing increase in atmospheric CO2 concentration tended to enhance the climate sensitivity of the carbon fluxes, by ~ 3% for γTemp and 2%-4% for γPrec, as a result of CO2 fertilization and water use efficiency improvement. The climate sensitivity heterogeneity revealed that interannual variation in Rh is more likely to be amplified than NPP or NEP. The findings imply that climate change exerts a strong influence on the carbon dynamics of the alpine ecosystem in the Tibetan Plateau, and this could further modulate the carbon balance depending on the magnitude of different carbon component fluxes. Our study suggests that changes in the climate sensitivity of carbon dynamics should be considered to further quantify the carbon dynamics in this climate-sensitive region.