Effects of Iron and Zinc Fertilizers on Antioxidant Activity of Pear-Jujube in Loess Hilly Region

With eight-year-old pear-jujube trees with uniform and good growth as the research object, different concentrations of iron and zinc fertilizers were sprayed to the leaves, and the changes in the contents of vitamin C, total flavonoids, enzyme, as well as the removal rates of hydroxyl radicals, 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) and hydrogen peroxide by polyphenols in pear-jujube were studied, so as to explore the effects of iron and zinc fertilizers on antioxidant activity of pear-jujube in loess hilly region. The results showed that different treatments affected the content of vitamin C and significantly increased the content of total flavonoids in pear-jujube. In the treatment of 0.6% FeSO4+0.3% ZnSO4 (L3), the contents of vitamin C and total flavonoids were both highest, 2.86 mg/g and 3.02 mg/g, 21.8% and 105.4% higher than CK (P<0.05). Different fertilization treatments effectively reduced the activities of ascorbate oxidase and polyphenol oxidase in pear-jujube. The activity of ascorbate oxidase was lowest in the treatment of 0.6% FeSO4+0.3% ZnSO4 (oxidized ascorbic acid 0.069 mg/(g·min) FW), 75.1% lower than CK); and the activity of polyphenol oxidase was lowest in the L3 treatment (oxidized ascorbic acid 0.146 mg/(g·min) FW, 42.0% lower than CK). Polyphenols of pear-jujube could effectively remove hydroxyl radicals, DPPH· and hydrogen peroxide. This was more significant in L3 treatment, of which the antioxidant activity was the best.