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

Taking the potted seedlings of Camellia salicifolia var. weniensis as the material, two conditions, namely normal temperature treatment and low-temperature stress, were set up. The effects of different exogenous sugar spray treatments on the hormone content, photosynthetic parameters and leaf anatomical structure of the oil tea leaves were analyzed. The results showed that the two-factor analysis indicated that temperature and exogenous sugar treatment had significant effects on the content of gibberellin, some photosynthetic parameters and leaf anatomical indicators. Under low-temperature stress, compared with CK, exogenous galactose could significantly increase the content of indoleacetic acid. Low temperature inhibited the net photosynthetic rate of Camellia salicifolia var. weniensis, but the net photosynthetic rate significantly increased under the treatments of exogenous galactose, trehalose and mixed sugar. In addition, exogenous galactose treatment significantly increased the thickness of the upper epidermis, palisade tissue thickness and tissue compactness of the leaves under low-temperature conditions. The changes in the microscopic structure of the oil tea leaves were significantly correlated with the photosynthetic indicators, while the correlation between abscisic acid and photosynthetic parameters and leaf anatomical indicators was not significant. Therefore, exogenous sugar treatment significantly improved the cold tolerance of Camellia salicifolia var. weniensis by improving the leaf anatomical structure and photosynthetic performance, and the effect of exogenous galactose treatment was better than that of other exogenous sugar treatments.