Primary Research On The Effect Of Light Intensity On Five Evergreen Broad-leaved Seedlings

Evergreen broad-leaved forest in China is one of the main typical evergreen broad-leaved forests under subtropical humid climatic conditions. Human-induced disturbances in the last several decades have destroyed most of the vegetation of the type in our country. The ecolgical function of Evergreen broad-leaved forest is very weak. How to restore the vegetation of Evergreen broad-leaved forest in China, and change of the trend of ecological deterioration is a very important issue. Light is one of the most important environmental factors, it limits the subsistence, growth of plant and community sucession in the forest. Through studying effect on the plants to different light intensity we can learn more about Evergreen broad-leaved forest renewal and succession.A controlled experiment was conducted in Zhejiang Forestry College experimental base, make the simulated light environments in accordance with three different light intensity. The selected materials were Schima superb, Lithocarpus glabra, Castanopsis sclerophylla, Cyclobalanopsis glauca and Elaeocarpus sylvestris (Lour).Poir, two years old seedlings, belonging to subtropical Evergreen broad-leaved species in Zhejiang province.The material were planted in abandoned lands. In this study, I explored the change of growth and photosynthesis under different light levels.The results showed that:(1) Low light intensity favored the height growth of Elaeocarpus sylvestris (Lour).Poir.and restrained the ground diameters. however, Schima superb, Lithocarpus glabra, Castanopsis sclerophylla and Cyclobalanopsis glauca growed slowly under low light intensity.(2) Light intensity has effects on leaf characters of five plant seedlings. With the gradual decrease of light intensity, the SPADR value of five plants leaves all went up. It was advantageous to improve of Pn under low light intensity. The SPADR value of five plants leaves in September was the highest among three measurement seasons. The specific leaf weight (SLW) of five plants decreased gradually and the RWC went up with the decrease of light intensity. Under full light Schima superb showed the highest SLW.(3) Light intensity has effects on photosynthesis of five plant seedlings, the chlorophyll II fluorescence parameters (Fv/Fm, Fv/Fo) of five plants under low light intensity were higher that those under full light intensity in two measurement seasons. With the gradual decrease of light intensity the maximum net photosynthetic rate (Amax), light compensation point (LCP), light saturation point (LSP) and the dark respiratory rate (Rd) of five plants went down. All of which were adaptive response to the low light intensity. Under full light treatments, Amax and LCP of Schima superb were the highest among all the plants, suggesting that Schima superb has better adaptation to high light intensity. Under 15% full light intensity treatments, Amax of Schima superb in September was lowest and LCP of Schima superb was highest among them in September, suggesting that Schima superb showed worse adaptation to low light intensity than the late–succssional species.(4) The average of phenotypic plasticity index for the structural and physiological parameters of Schima superb (early-successional species) was higher than Lithocarpus glabra, Castanopsis sclerophylla, Cyclobalanopsis glauca and Elaeocarpus sylvestris (Lour.) Poil(late-successional species). And the results also supported the hypothesis that ecophysiological traits of tree species determined their successional status.