Effects of Exogenous Sugar Treatment on Hormone Levels, Photosynthetic Parameters, and Leaf Structure of Camellia weiningensis Seedlings under Low-Temperature Stress

This study used potted Camellia weiningensis seedlings as experimental material to investigate the effects of different exogenous sugars(50 mM sucrose, 10 mM galactose, 10 mM trehalose, and mixed sugars) sprayed on hormone content, photosynthetic parameters, and leaf anatomical structure of leaves. The experiment was conducted under two conditions: normal temperature treatment(25 ℃/20 ℃, day/night) and low-temperature stress(10 ℃/5 ℃, day/night). Results showed that both temperature and exogenous sugar treatments significantly affected gibberellin(GA) content, photosynthetic parameters, and leaf anatomical indices. Under low-temperature stress, compared with the water-sprayed control(CK), exogenous galactose significantly increased the content of IAA. Low temperature inhibited the net photosynthetic rate(Pn) of C. weiningensis, but Pn values significantly increased under exogenous galactose, trehalose, and mixed sugar treatments. In addition, exogenous galactose treatments significantly increased the thickness of the upper epidermis, palisade tissue, and tissue compactness of the leaves. Correlation analysis indicated that changes in leaf microstructure were significantly correlated with photosynthetic parameters, while endogenous hormone ABA content showed no significant correlation with photosynthetic parameters or leaf anatomical indices. In conclusion, exogenous sugar treatments significantly enhanced the low-temperature tolerance of C. weiningensis by improving leaf anatomical structure and photosynthetic performance. The treatment with exogenous galactose is more effective than treatments with other exogenous sugars.