Abstract
The Tibetan Plateau is an important component of the global carbon cycle due to the large permafrost carbon pool and its vulnerability to climate warming. The Tibetan Plateau has experienced a noticeable warming over the past few decades and is projected to continue warming in the future. However, the direction and magnitude of carbon fluxes responses to climate change and elevated CO2 concentration under Representative Concentration Pathways (RCP) scenarios in the Tibetan Plateau grassland are poorly known. Here, we used a calibrated and validated biogeochemistry model, CENTURY, to quantify the contributions of climate change and elevated CO2 on the future carbon budget in the alpine grassland under three RCP scenarios. Though the Tibetan Plateau grassland was projected a net carbon sink of 16 ~ 25 Tg C yr-1 in the 21st century, the capacity of carbon sequestration was predicted to decrease gradually because climate-driven increases in heterotrophic respiration (Rh) (with linear slopes 0.49 ~ 1.62 g C m-2 yr-1) was greater than the net primary production (NPP) (0.35 ~ 1.52 g C m-2 yr-1). However, the elevated CO2 contributed more to plant growth (1.9% ~ 7.3%) than decomposition (1.7% ~ 6.1%), which could offset the warming-induced carbon loss. The interannual and decadal-scale dynamics of the carbon fluxes in the alpine grassland were primarily controlled by temperature, while the role of precipitation became increasingly important in modulating carbon cycle. The strengthened correlation between precipitation and carbon budget suggested that further research should consider the performance of precipitation in evaluating carbon dynamics in a warmer climate scenario.
Highlights
The distinctive geographic environment of the world highest plateau—Tibetan Plateau makes its carbon cycle be strongly sensitive to climate variation and environmental change [1,2,3]
The CENTURY model predicted that the grass net primary production (NPP) would range from 308 ± 13 g C m-2 yr-1 to 495 ± 21 g C m-2 yr-1, with a multiyear mean NPP of 357 ± 18 g C m-2 yr-1 for RCP2.6, 375 ± 20 g C m-2 yr-1 for RCP4.5, and 408 ± 26 g C m-2 yr-1 for RCP8.5 on the Tibetan Plateau, respectively (Fig 2A)
The alpine grasslands of the Tibetan Plateau behaved as a carbon sink, with a simulated net ecosystem production (NEP) on a range of 11 ± 16 g C m-2 yr-1, 15 ± 16 g C m-2 yr-1, and 18 ± 16 g C m-2 yr-1 for RCP2.6, RCP4.5, and RCP8.5, respectively, for the period from 2006~2100 (Fig 2C)
Summary
The distinctive geographic environment of the world highest plateau—Tibetan Plateau (with an average elevation of over 4000 m above sea level) makes its carbon cycle be strongly sensitive to climate variation and environmental change [1,2,3]. The Plateau covers a vast area of alpine vegetation and has a large reservoir of organic carbon in the permafrost soil, and it has been reported as a significant terrestrial carbon sink for recent decades due largely to warming and CO2 fertilization [3,4,5]. Increasing temperatures have been reported to prolong growing season lengths [6], metabolic rates, and the productivity and distribution [7] of vegetation at the Plateau and high latitude areas [8,9,10]. Schaphoff et al [15] revealed that warming contributed to the net uptake of carbon in the permafrost zone in previous decades because carbon uptake by vegetation increased at a faster rate than that released from soil. Increasing the atmospheric CO2 concentrations tends to stimulate photosynthesis and reduce water loss [16,17], which is likely to offset the adverse effects of climate change
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