Effects Of Drought And Phosphorus Deficiency On Photosynthesis Of Winter Rape

Photosynthesis is the basis for the formation of crop yield. Photosynthesis is the most sensitive physiological process for crop to response to various environmental factors. Both drought and phosphorus deficiency are important constraint factors in rapeseed production. In order to investigate the physiological mechanism of photosynthesis of the rapeseed at different growth stages under double stresses of drought and phosphorus deficiency, explore the critical period of the respectively impact of the rapeseed`s photosynthesis under drought and phosphorus deficiency, prove up the interaction of water and phosphorus nutrition on photosynthesis, and provide a theoretical basis for the physiological regulation of photosynthesis and the development of disaster mitigation measures at adverse conditions. Zhongshuang No.9 was applied to research the changes and the gas exchange parameters, chlorophyll content, fluorescence dynamics parameter, malondialdehyde content(MDA), as well as the activity of superoxide dismutase(SOD) under drought and phosphorus deficient stresses were determined. The results were as follows.:(1) Photosynthesis parameters at stem elongation and flowering stage of winter rape were changed significantly under the double stresses, while the parameters were not changed significantly at the seedling stage. The net photosynthetic rate (Pn) was decreased significantly at stem elongation and flowering stage of the rapeseed under the double stresses. Through the analysis of intercellular CO2 concentration (Ci) and stomatal limitation value (Ls),we found that non-stomatal factors were mainly contributed to Pn decreasing. The most effect period of phosphorus deficiency on Pn of rapeseed leaves was in stem elongation stage, while flowering stage was the most effect period for drought stress. And yield and yield components of rapeseed were observably reduced under the double stresses. Moreover the extent of rapeseed production is declined by 62.92%.(2) The chlorophyll contents of winter rape were decreased during the three periods under the double stresses of drought and phosphorus deficiency. Fv/Fm,ФPSⅡ,ETR,qP were all decreased, but Fo and NPQ were increased at stem elongation and flowering stage under stresses, indicating that stresses played a great role in regulating Photosynthesis of rapeseed. The reason might be that stresses caused photoinhibition, by inhibiting the primary reaction of photosynthesis, causing damage of the active central of PSⅡ, reducing the openness of PSⅡreaction center and electron transport activity, enhancing heat dissipation capacity, and reducing the damage to the photosynthetic apparatus due to excessive light energy absorbed by PSⅡ.(3) The results indicated that MDA content increased and SOD activity declined a lot under stresses, meaning that the cell membrane structure of rapseed was damaged under stresses.(4) In addition, we found that the impact of double stresses on rapeseed was significantly higher than that of single-factor stress, the effects of drought and phosphorus deficiency could strengthen each other, showing obvious stress superposition effect. The amount of phosphorus nutrition could mitigate the effect of drought stress on rapeseed. In contrast, the appropriate moisture could reduce phosphorus deficiency on rapeseed. Thus we speculated that it existed closely relation between phosphorus nutrition and water.