Optimal temperature of vegetation productivity and its linkage with climate and elevation on the Tibetan Plateau

Abstract

Vegetation productivity first increases and then decreases with temperature; and temperature corresponding to the maximum productivity is called optimal temperature (T_opt ). In this study, we used satellite derived near-infrared reflectance of vegetation (NIR_v ) data to map T_opt of vegetation productivity at the spatial resolution of 0.1° on the Tibetan Plateau (TP), one of most sensitive regions in the climate system. The average T_opt of non-forest vegetation on the TP is about 14.7°C, significantly lower than the T_opt value used in current ecosystem models. A remarkable geographical heterogeneity in T_opt is observed over the TP. Higher T_opt values generally appear in the north-eastern TP, while the south-western TP has relatively lower T_opt (<10°C), in line with the difference of climate conditions and topography across different regions. Spatially, T_opt tends to decrease by 0.41°C per 100 m increase in elevation, faster than the elevational elapse rate of growing season temperature, implying a potential CO₂ regulation of T_opt in addition to temperature acclimation. T_opt increases by 0.66°C for each 1°C of rising mean annual temperature as a result of vegetation acclimation to climate change. However, at least at the decadal scale, there is no significant change in T_opt between 2000s and 2010s, suggesting that the T_opt climate acclimation may not keep up with the warming rate. Finally, future (2091-2100) warming could be close to and even surpass T_opt on the TP under different RCP scenarios without considering potential climate acclimation. Our analyses imply that the temperature tipping point when the impact of future warming shifts from positive to negative on the TP is greatly overestimated by current vegetation models. Future research needs to include varying thermal and CO₂ acclimation effects on T_opt across different time scales in vegetation models.

Keywords: Tibetan Plateau; elevational dependence; geographical heterogeneity; near-infrared reflectance of vegetation; optimal temperature; thermal acclimation.