Response of Photosynthetic Pigments in Two Dominant Plant Species to Precipitation Changes in the Yuanjiang Dry-Hot Valley

Against 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. This study was conducted at a savanna in-situ precipitation manipulation platform established in the Yuanjiang dry-hot valley. The platform comprised seven treatments: a control, precipitation exclusion of 30%, 50%, and 70%, and precipitation addition of 30%, 50%, and 70%. We systematically investigated the responses of leaf photosynthetic pigments in two dominant species, Lannea coromandelica and Polyalthia cerasoides, to these precipitation gradients. Compared to precipitation addition treatments, both species significantly increased chlorophyll and carotenoids contents under extreme drought condition (70% precipitation exclusion). However, they exhibited distinct regulatory patterns. L. coromandelica maintained a stable chlorophyll a/b but reduced the proportion of carotenoids under 30% precipitation exclusion. 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 reveal that the two species employ different photosynthetic adjustment pathways to cope with drought stress: L. coromandelica adopts an active photosynthetic investment strategy, whereas P. cerasoides exhibits a more conservative adaptive trait. The results not only elucidate the diversity of physiological adaptations in woody plants within natural drought habitats, but also provide a crucial scientific basis for vegetation restoration and the selection of stress-adapted tree species in this region.