Effects of Sub-chilling Stress in Spring on Photosynthetic Physiological Characteristics of Camellia Oleifera ‘Huashuo’ Leaves

To explore the effects of sub-chilling stress on the photosynthetic characteristics of Camellia oleifera leaves, 2-year-old potted seedlings of Camellia oleifera ‘Huashuo’ were used as the test material. The rapid chlorophyll fluorescence induction curve and 830 nm light absorption curve as well as ultrastructure of Camellia oleifera leaves under sub-chilling stress (10 ℃/5 ℃) were measured, and the effects of chlorophyll content, photosystem activity and carbon assimilate content were analyzed. Compared with the normal temperature（28 ℃/20 ℃), the chlorophyll contents, PSII and PSI photoinhibition occurred in the leaves of Camellia oleifera under sub-chilling stress. The rapid chlorophyll a fluorescence induction curve analysis showed that photosynthetic mechanism electron transfer chain of Camellia oleifera were inhibited in varying degrees under sub-chilling stress, resulting in a decrease of photosynthetic performance. In addition, with the extension of the sub-chilling stress treatment time, the relative conductivity, the soluble sugar content increased, but the starch content gradually decreased. This study shows that, under sub-chilling stress, excess excitation can inhibit the activities of PSII and PSI of Camellia oleifera, resulting in the decrease of photosynthetic electron transfer activity. And the cell membrane system got further damaged as the stress prolonged. However, within a certain period of time, the photosystems activities of Camellia oleifera leaves could maintain stable by accumulating soluble sugar contents.