Vegetation photosynthesis changes and response to water constraints in the Yangtze River and Yellow River Basin, China

Abstract

• Spatio-temporal pattern of annual maximum GOSIF were evaluated. • Water deficit area had an expanding trend, water surplus area had a shrinking trend. • The r GOSIF-scPDSI and r GOSIF-SPEI03 variations can be explained by atmospheric CO 2 . Satellite remotely sensed solar-induced chlorophyll fluorescence (SIF) is an effective index for detecting the ecosystem-level photosynthetic capacity, yet it remains poorly understood how vegetation photosynthesis responds to water constraints. This study determined the spatial–temporal changes and water constraints on vegetation photosynthesis based on the Self-Calibrated Palmer Drought Severity Index (scPDSI), Standardized Precipitation Evapotranspiration Index (SPEI) and global Orbiting Carbon Observatory-2 SIF (GOSIF) data in the Yangtze River and Yellow River basin between 2000 and 2018. The results showed that annual maximum GOSIF steadily increased across the whole basin ( slope = 0.0031 W m -2 μm -1 sr -1 a -1 , P < 0.001). The maximum increasing trend was found in the semi-arid region (0.0034 W m -2 μm -1 sr -1 a -1 , P < 0.001). The highest value of annual maximum GOSIF was found in the Qinling-Daba Mountains along with Hengduan Mountain. The lowest GOSIF was found in the western portions of the Loess Plateau and the source region of Yangtze River and Yellow River. Positive correlations between satellite GOSIF and water availability were particularly strong in the Loess Plateaus; in contrast, negative correlations were found in the Hengduan Mountains. The area of water deficit displayed a significant trend towards expansion ( slope = 1.539 % a -1 and 0.898 % a -1 , P < 0.05), while water surplus areas significantly shrank ( slope = 0.847 % a -1 and 0.584 % a -1 , P < 0.05) in the Yangtze River and Yellow River basin. Atmospheric CO 2 concentration and precipitation were the dominant drivers for the water deficit regions, while atmospheric CO 2 concentration and temperature were the dominant drivers for the water surplus regions. This study emphasizes the effect of water constraints on regional vegetation photosynthesis under global warming conditions and patterns of greening.