Effects of soil moisture on photosynthetic rate, transpiration rate and water use efficiency of rape in different leaf positions

The difference of the net photosynthetic rate (Pn),transpiration rate (E) and water use efficiency (WUE) of rape in different leaf positions on stem was observed under different soil moistures. It was found that net photosynthetic rate, transpiration rate and water use efficiency decreased with the drop of leaf position. Under the water stress,net photosynthetic rate showed an increasing trend but not significant and transpiration rate decreased while water use efficiency increased significantly. The difference of net photosynthetic rate between the upper leaves and the lower one s was great and the difference of transpiration rate between the upper leaves and the lower ones was not significant. Under the condition of full irrigation, the transpiration rate increased, and net photosynthetic rate and water use efficiency decreased.Transpiration rate was higher in upper and lower leaf positions,lower in middle leaf position.According to determination, under the condition of drought and full irrigation the biomass of single plant rape was 37.45g and 38.76g respectively. Drought leads to drop of rape biomass. Water stress could increa se the water use efficiency. Under the condition of full irrigation, the transpiration rate of leaf was higher, this may be the result of stomatic behaviour.