Effect of nitrogen nutrition on physiological index of spinach senescence

A field pilot study was carried out to study the effects of nitrogen nutrition on spinach senescence.The results showed that the root vigor,chlorophyll content,photosynthetic rate and superoxide dismutase(SOD),peroxidase(POD),catalase(CAT) activities increased at the early growth period of spinach,but decreased stably later;the electrolyte leakage and malondiadehyde(MDA) content continually increased within the whole growth period.However,when nitrogen applied rate was less than 600 kg/ha,nitrogen fertilization significantly reduced the electrolytic leakage and MDA content,enhanced SOD,POD,CAT and chlorophyll content and photosynthetic rate of spinach leaves,promoted root vigor and delayed the senescence,furthermore,increased the yield of spinach.At the time of spinach harvest,the electrolytic leakage and MDA contents of the treatment,which applied 600 kg/ha nitrogen,were 50.9% and 67.2% lower than that of CK(without N),respectively.Nevertheless,the SOD,POD,CAT and root vigor were 59.2%,478.4%,290.9% and 131.3% higher than that of CK,the photosynthetic rate and chlorophyll content also increased by 59.6%,131.3%,and the yield increased by 88.0%.Applying nitrogen 900 kg/ha resulted in a negative effect.Although it increased the yield by 75.3% compared to CK,it decreased yield by 6.7% compared to the treatment with applying nitrogen 600 kg/ha.