Effects Of Shading On Photosynthetic Characteristics And Growth Of Vetiveria Zizanioides In Western Guangdong

Effects of three levels of shading (no shading, 75%shading, 94%shading) during different growth period(seedling period, rapid growth period and tasseling period) on photosynthetic characteristics and growth of vetiver grass (Vetiveria zizanioides) were studied in western Guangdong.Photosynthetic characteristics, chlorophyll content, biomass and other growth characters indexes relation to growth and development were measured. The effects of shading on the growth and photosynthetic characteristics were discussed emphatically. The results indicated:1,Net photosynthetic rate (Pn) was decreased significantly(p<0.05) during seedling period by shading and the values of Pn under 75% and 94% shading were 58.43% and 31.26% of the control (15.13μmolm-2s-1) respectively.Also transpiration rate (Tr) and water use efficiency (WUE) under 94% shading were decreased obviously, while intercellular CO2 concentrations (Ci) was increased remarkably (p<0.05). During tasseling period ,shading caused a decrease of light saturation point(LSP)and the light compensation point (LCP)to some degree, and the light compensation poin(tLCP)under 75% and 94% shading were decreased by 13.42% and 56.82% of the control (46.94μmol·m-2·s-1 ) respectively. It was very significantly different (p<0.01) between the 94%shading treatment and the control, but the apparent quantum efficiency (AQY) was increased by shading to different degree.2,After 30 days shading on vetiver grass in rapid growth period .The content of chlorophyll a, chlorophyll b and total chlorophyll were increased significantly under shading treatments, and total chlorophyll content of 75% and 94% shading were increased by 29.70% and 19.31% of the control (2.02mg/g) respectively. However, the ratio of chlorophyll a and chlorophyll b was not obviously different among three treatments. The change treadency of the content of chlorophyll at tasseling period and rapid growth period under shading was consistent.3,As the intensity of illumination reduced, tiller number was decreased significantly (p<0.05) at three growth period after shading, and it under 75% and 94% shading were reduced by 62.33% and 64.13% of the control (21.58per plant) at rapid growth period. Total dry matter per plant under 75% and 94% shading were decreased by 67.82% and 76.58% of the control (22.50g) respectively at seedling period. Total biomass increments under 75% and 94% shading were 32.44% and 32.10% of the control (126.44g) respectively at rapid growth period, and the total dry matter was decreased by 41.75% of the control at tasseling period.4,Effects of shading on water content at three growth period were different. The influence of shading on water content was very small at seedling period, but it reached obviously (p<0.05) different at rapid growth period and tasseling period.During tasseling period, the water content of plant under 75% and 94%shading were increased by 5.76% and 15.40% of the control, and the heavy shading degree (94%shading) and the control appeared extremely different (p<0.01).