Integrated physiological, biochemical, and transcriptomic analyses reveal changes in photosynthetic capacity of the endangered tree Cinnamomum chago under water stress.

Cinnamomum chago, an endangered tree endemic to Yunnan Province, China, is a valuable resource for edible nuts, timber, and oil, with both economic and ecological significance. However, natural regeneration of C. chago seedlings is challenging, and sustainable cultivation strategies are needed to balance economic development and ecological conservation. Here, we investigated physiological, biochemical, and transcriptomic responses of C. chago seedlings to water stress. Net photosynthetic rate (5.136 to 0.322 μmol▪m^-2s^-1), transpiration rate (1.064 to 0.151 mmol▪m^-2s^-1), water-use efficiency (5.107 to 1.459 mmol▪mol^-1H₂O), Rubisco maximum carboxylation rate (21.269 to 1.393 μmol▪m^-2s^-1), and maximum electron transport rate (20.950 to 1.483 μmol^-1 m^-2·s^-1) decreased under drought. The reduction in photosynthetic rate under water stress was likely associated with non-stomatal limitations inferred from Ci patterns. In contrast, proline (1.198 to 10.977 umoles▪g^-1), soluble sugars (0.272 to 0.448 umoles▪g^-1FW), superoxide dismutase (25.901 to 59.966 U▪g^-1FW), and malondialdehyde (0.036 to 0.043 μmol▪g^-1FW) showed significant increases (p < 0.05). Transcriptomic analysis revealed significant enrichment of photosynthesis, flavonoid and phenylpropanoid biosynthesis, and hormone signaling pathways (p < 0.05), with downregulation of genes involved in light capture and energy conversion, which was consistent with reduced photosynthetic performance. Overall, these results indicate that drought stress significantly reduce photosynthetic capacity. Maintaining soil moisture at 75-80% appeared to be optimal under short-term greenhouse cultivation and may provide a reference for future studies. These findings provide insights into the physiological and molecular mechanisms underlying drought responses in C. chago and inform management of endangered woody plants.