Response of photosynthetic pigments in two dominant plants to precipitation changes in Yuanjiang dry-hot valley

In the context of intensifying drought due to climate change, the adaptive strategies of leaf photosynthetic pigments in woody species to combined drought stress remain unclear. In this study, an experimental platform for in-situ precipitation manipulation at a savanna was set up in Yuanjiang dry-hot valley, and seven treatments were set up, including control, precipitation reduction by 30%, 50%, and 70%, and precipitation addition by 30%, 50%, and 70%. The responses of leaf photosynthetic pigments in two dominant species, Lannea coromandelica and Polyalthia cerasoides, to these precipitation gradients were systematically investigated. Compared with the precipitation addition treatment, the two plants significantly increased the chlorophyll and carotenoid contents under extreme drought treatment (70% precipitation reduction). However, the difference was that L. coromandelica maintained a stable chlorophyll a/b but reduced the proportion of carotenoids under 30% precipitation reduction. In contrast, chlorophyll a/b of P. cerasoides increased under extreme drought while maintaining a stable carotenoids proportion, suggesting an optimized allocation of light energy. Furthermore, P. cerasoides consistently exhibited higher photosynthetic pigment levels than L. coromandelica across all treatments. These findings revealed that the two plants employed different photosynthetic adjustment pathways to cope with drought stress: L. coromandelica adopt an active photosynthetic investment strategy, whereas P. cerasoides exhibited a more conservative adaptive traits. The results not only elucidated the diversity of physiological adaptations in woody plants within natural drought habitats, but also provided a crucial scientific basis for vegetation restoration and the selection of stress-adapted tree species in this region.