Impacts of climate and CO_2 changes on the vegetation growth and carbon balance of Qinghai-Tibetan grasslands over the past five decades

摘要

Climate change has significantly influenced global and regional terrestrial carbon balances. After being systematically calibrated against eddy-covariance measurements, meteorological observation, soil inventory data and satellite observed LAI (Leaf Area Index) in the Qinghai-Tibetan Plateau (Tan et al., 2010), the process-based ecosystem model called ORCHIDEE (ORganizing Carbon and Hydrology In Dynamic EcosystEms) was used in this study to investigate climate change and rising atmospheric CO_2 concentration driven spatio-temporal changes in vegetation net primary production (NPP) and net ecosystem production (NEP) of Qinghai-Tibetan grasslands from 1961 to 2009. Overall, our simulation suggests that Qinghai-Tibetan grassland NPP significantly increased with a rate of 1.9 Tg C yr~(-2) (1 Tg= 10~(12) g) since 1961. At the regional scale, change in precipitation, temperature, and atmospheric CO_2 concentration accounts for 52%, 34%, 39% of the increase in NPP, respectively, but their relative roles are not constant across the study area. Increase in NPP over the central and southwestern Qinghai-Tibetan Plateau is primarily attributed to precipitation changes, while rising atmospheric CO_2 concentration is the main cause of NPP increase in eastern plateau. The model simulation also suggests that Qinghai-Tibetan grassland NEP increased from a net carbon source of -0.5 Tg C yr~(-1) in the 1960s to a net carbon sink of 21.8 Tg C yr~(-1) in the 2000s, mainly due to the rising atmospheric CO_2 concentration and precipitation change. Although recent climate warming benefited vegetation growth, rising temperature did not significantly accelerate net carbon uptake from Qinghai-Tibetan grassland ecosystems due to enhanced soil carbon decomposition accompanying increase in temperature.