Effects Of Shading On Vegetative Growth And Photosynthetic Physiological Ecology Of Cymbidium Longibracteatum

In this study, growth of aboveground and sprout were observed, changes of photosynthetic characteristics, antioxidant defense system related substances and organic compounds were investigated of three Cymbidium longibracteatum cultivars'Yingansu', 'Honghuachunjian' and'Dahongzhusha' under different shade treatment (30% shade,65% shade,80% shade,90% shade). The effects of different shade degree on vegetative growth and photosynthetic physiology ecology of Cymbidium longibracteatum were investigated. Results showed as below:(1)Under 30% and 65% shade degree, shorter and narrower leaves, smaller amount and slower growth of new budlets for three cultivars of Cymbidium longibracteatum were found. However, leaves of 80% and 90% shade degree were bigger and widener, and amount of new budlets was bigger than 30% and 65% shade degree significantly.(2) Under 30% and 65% shade degree, the peak value for photosynthetic rate was appeared in spring, which was 1.6-2.7 umol·m-2·s-1.While, a sharpdecline of photosynthetic rate were found in summer (except 'Dahongzhusha'). The light, CO2 compensation point increased gradually. The light saturation point, apparent quantum efficiency and carboxylation efficiency decreased gradually, and there was also a significant difference for chlorophyll fluorescence parameters, such as Fo, Fv/Fm, and showed light inhibition. Under 80% and 90% shade degree, the peak value of photosynthetic rate was significantly higher than 30% and 65% shade degree, and other photosynthetic parameters showed smaller change. Stronger ability to capture light energy and higher CO2 assimilation capacity were shown in 80% and 90% shade.(3) Antioxidant enzymes and memnrane peroxidation has complicated change under different shade degree. The highest of POD and SOD activities, and minimum of MDA contents were observed at 90% shade degree of'Yingansu',80% shade degree of 'Honghuachunjian' and 'Dahongzhusha'(Jul.to Aug.). POD and SOD activities of 30% and 65% shade degree were lower than 80% and 90% shade degree significantly, while MDA contents were higher than 80% and 90% shade degree significantly.(4) The change of soluble protein and soluble sugar were complex.However, the contents of soluble protein and soluble sugar of 80% and 90% shade degree significant were higher than 30% and 65% shade degree at Jul.to Aug.. The peak value of soluble protein and soluble sugar content were observed in 90% shade degree of'Yingansu'and 80% shade degree of'Huachunjian'and'Dahongzhusha'.(5) Under 30% and 65% shade degree, the content of chlorophyll for Cymbidium longibracteatum decreased significantly, and the leaves became yellow, soft, losing their luster and hardness. Under 80% and 90% shade degree, the content of chlorophyll showed stable, and leaves were shiny.30%～90% shade degree all can be choose for'Yingansu' at Feb. to Mar..The optimum shade degree for'Yingansu' was 90% during Apr. to Aug. and 80% shade degree for'Honghuachunjian' and 'Dahongzhusha'.