Effect of Shading on Seasonal Change of Physiology and BIochemistry of YulanIa sinostellata Seedlings

In early January 2020, two-year Yulania sinostellata seedlings were transplanted in pot in Linhai, Zhejiang province. Experiments were conducted on seedlings by full light intensity (I100) (CK), shading of 40% (I40) and 10% (I10) of natural light intensity. Net photosynthetic rate (Pn), photosynthetically active radiation (PAR) and photosynthetic pigment of treated seedlings was determined on April 17th, July 12th and October 15th 2020. The result showed that Pn of the control was significantly higher than that under I40 and I10 in spring, and that under I40 was significantly higher than that of the control and I10 in summer and autumn. Pn of the control and I40 was significantly higher in summer than in spring and autumn, while Pn of I10 was significantly lower in summer than in spring and autumn. Chlorophyll (Chl) content had positive relation with shading intensity in the experimental period, while carotenoid/chlorophyll (Car/Chl) had negative one. The chlorophyll and carotenoid contents of treated seedlings were the highest in spring, and the chlorophyll a/b (Chl a/b) and Car/Chl were the highest in summer. The activity of superoxide dismutase (SOD) decreased with the increase of shade intensity in spring and autumn. The peroxidase (POD) activity increased with the increase of shade intensity in summer and autumn, and the catalase (CAT) activity was lower in the control. SOD activity was the highest in autumn, POD and CAT activity was the highest in spring under the three shade treatments. The content of ascorbic acid (AsA) in three seasons was the lowest under I10 treatment. The content of glutathione (GSH) was the highest in the control in summer and under I40 in autumn. The electrical conductivity of the control in summer was significantly higher than that under I10, and in autumn was significantly higher than that under I40 and I10. The electrical conductivity of treated seedlings was the highest in autumn and the lowest in spring with significant difference. The experiment demonstrated that chlorophyll content of Y. sinostellata seedlings of the control was lower in summer and autumn, and POD and CAT activities were weaker, which could not effectively remove reactive oxygen, causing increase of cell membrane permeability and light stress on leaves. However, seedlings under I10 had lower photosynthetic capacity.