Evidence and patterns of decreased sensitivity of vegetation leaf photosynthetic efficiency to precipitation

The sensitivity of vegetation to climate is an important indicator for measuring changes in plant production and predicting future ecosystem functions in the context of global change. However, the sensitivity of global vegetation photosynthetic capacity to precipitation has not been studied. In this study, we defined vegetation leaf photosynthetic efficiency (LPE) using the ratio of gross primary productivity to leaf area index. We used multiple regression to establish the sensitivity coefficient ( S _p ) of LPE to precipitation and then explored how S _p has evolved in space and time across the world's climate zones and land biomes from 1982 to 2018. We also used random forest and multi-scenario simulations of dynamic vegetation models to investigate the driving mechanism of the changes in S_p. Results indicated that S _p was higher in arid zone and cropland. The S _p exhibited a significantly decreasing trend from 1982 to 2018 ( p < 0.05), with the most pronounced decreases observed in arid regions among various aridity gradients, and most occurred in croplands and pastures among different plant functional types. VPD was identified as the largest contributing factor to the decrease in S _p , followed by temperature and radiation, while soil moisture had a relatively small contribution to S _p change. Overall, CO₂, climate change and land use change may explain 36.2% 32.3% and 31.5% of the changes in S _p , respectively. The research results help deepen our understanding of the driving mechanisms of carbon cycling in terrestrial ecosystems, and are of great significance for ecosystem management and protection in the context of global change.