Response of Protective Enzyme Activity of Soybean Variety Leaves with Different Nitrogen Photosynthetic Efficiency to Nitrogen Application Levels

Response of protective enzyme activity of soybean variety leaves with different nitrogen photosynthetic efficiency to nitrogen application levels was studied. Under field conditions,using five nitrogen levels( 0,40,80,120,160 kg / hm2),leaf SOD activity,POD activity,CAT activity,MDA content and soluble protein content of leaves of two different soybean varieties( low nitrogen photosynthetic efficiency varieties and high nitrogen photosynthetic efficiency varieties) were researched at four growth stages( R2,R4,R6,R7). The results showed that in a certain range,with increasing amount of nitrogen,SOD,POD,CAT activity and soluble protein content were im-proved in different degrees,while MDA content was decreased. When nitrogen level exceeds a certain amount,however,protective enzyme activity and soluble protein content decreased,while MDA content was increased. In R6 and R7 growth periods,index characters of different nitrogen application levels were significantly different( P0. 05),indicating that a reasonable level of nitrogen plays an important role in maintaining high protective enzyme activity of soybean leaves in the late growth period. Different nitrogen photosynthetic efficiency variety had different response to nitrogen levels.In the case of high nitrogen photosynthetic efficiency varieties,protective enzyme activity and soluble protein content reached the maximum value and the minimum MDA content when nitrogen application was at the 80 kg / hm2 level. In the case of low nitrogen photosynthetic efficiency varieties,protective enzyme activity and soluble protein content reached the maximum value and the minimum MDA content when nitrogen application was at the 120 kg / hm2 level. The changes in yield of nitrogen levels were consistent with those of protective enzyme activity of different nitrogen photosynthetic efficiency varieties,so nitrogen photosynthetic efficiency could be used as a basis for selecting nitrogen application and determining the optimum amount of nitrogen.