Long-term dynamics of peak photosynthesis timing and environmental controls in the Tibetan Plateau monitored by satellite solar-induced chlorophyll fluorescence

Abstract

ABSTRACTVegetation phenological metrics have attracted increasing attentions during recent years. However, compared with the peak greenness timing (PGT), the peak photosynthesis timing (PPT) has been overlooked until now. As the world's third pole, the Tibetan Plateau is one of the most sensitive areas to global climatic change. In this study, long-term time-series solar-induced chlorophyll fluorescence (SIF) data were used to identify the PPT patterns, trends, and responses in the Tibetan Plateau over the past two decades. Our findings indicated that the SIF-derived PPT can better capture the characteristics from flux-measured gross primary productivity compared with the MODIS EVI-based PGT, exhibiting great potential to characterize large-scale vegetation PPT dynamics. The multi-year mean PPT mainly appeared in late July and early August with a gradually delayed trend from southeast to northwest. Meanwhile, early PPT occurred in many areas of the Tibetan Plateau (67.36%), with the overall trend advanced by about 0.89 day decade−1. Interestingly, opposite trends of PPT were found with elevation below and above 2500 m asl. Preseason temperature, shortwave radiation, and precipitation jointly explained the strong spatial heterogeneity of PPT trend. All analyses help clarify the role of the ‘third pole’ in responding to environmental change and regional carbon cycles.

Keywords

• Vegetation phenology
• peak photosynthesis timing
• global change
• eddy covariance
• Tibetan Plateau