Spatial variations in carbon dioxide fertilization effect on vegetation greening across the Tibetan Plateau

The impacts of shifting temperature and precipitation on vegetation dynamics in water-limited alpine ecosystems have been well-studied. However, there is a limited understanding of spatial variations in the carbon dioxide (CO₂) fertilization effect (CFE) on these systems. Here, using the MODIS normalized difference vegetation index (NDVI), meteorological and CO₂ gridded datasets from 2000 to 2022, we found that vegetation greenness showed an increasing trend in the Tibetan Plateau (TP), with a larger increasing trend in the north. Greenness changes were significantly positive correlated with temperature and precipitation in 10.13 % and 16.53 % of the TP respectively, mainly in center. In a smaller region in the southern TP, temperature and precipitation showed significant negative correlations, accounting for 2.22 % and 8.27 % of the TP respectively. Moreover, there were significantly positive relationships between greenness and CO₂ concentration in 23.69 % of the TP, suggesting that the CFE was more prevalent than the impacts of temperature and precipitation. In particular, the CFE was significant in 48.04 % of the alpine desert steppe. The spatial relationship between CFE and precipitation followed a unimodal pattern, peaking at an annual precipitation of 156 mm, and the CFE approached zero when precipitation exceeded 730 mm. In contrast, the relationship of CFE with temperature exhibited a bimodal pattern, peaking at mean annual temperatures of 2.1 °C and 12.7 °C. Their complex relationships should be closely related to the response of plant physiological processes to temperature and water. This study improved our understanding of vegetation response to global change in water-limited alpine ecosystems.