2019 ASHS Annual Conference

Due to its high photosynthetic efficiency, tung tree (Vernicia fordii) is a fast-growing heliophile, yielding fruit within 3 years. Additionally, tung oil extracted from the fruit seeds is an environmentally friendly paint widely used in China. However, mutual shading inside a tung tree canopy leads to a low yield of fruits due to weak or dead low branches. In this project a pot experiment was conducted to understand the growth, physiological and biochemical responses of tung trees under various shading levels. Tung tree seedlings were subject to different light intensities, i.e. L100 (control): 100% sunlight (no cover), L75: 75% sunlight (25% shading), L50: 50% shading, and L20: 20% sunlight (80% shading) from June to August. Results indicated that L75 treatment significantly reduced the net photosynthetic rate, stomatal conductance, transpiration rate, total aboveground and root dry mass, maximum net photosynthetic rate (A_max), and maximum rate of electron transport at saturating irradiance (J_max) compared to the control, although plant height and leaf area were not reduced. Lower light intensitis (L50 and L20) and longer duration of treatment led to greater reduction in growth and photosynthetic potential (A_max and J_max). Chlorophyll a, chlorophyll b, and total chlorophyll content were increased in L50 and L20 in comparison to those in L100 and L75. There was no significant reduction in the enzyme activities of ribulose-1,5-bisphosphate carboxylase (Rubisco) and phosphoenolpyruvate (PEPC) of the seedlings by the L75 treatment; however, lower light intensities (L50 and L20) and longer duration of shade treatment resulted in significant reduction in enzyme activity. In summary, our results suggest that tung tree has higher photosynthetic activity under high light intensity. However, shading, even at 20%, especially for longer term, reduced photosynthetic efficiency and growth. To prevent growth reduction, tung trees should be grown under full sun with a daily light integral of approximately 46 mol·m^-2·d^-1 and mutual shading should be avoided by proper spacing and pruning.