[Effects of different NO3- concentrations on the growth and antioxidant enzyme systems of strawberry seedlings].

The effects of different NO3- concentrations (CK, 16 mmol x L(-1) NO3-; T1, 48 mmol x L(-1) NO3-; T2, 96 mmol x L(-1) NO3-; T3, 144 mmol x L(-1) NO3-) on the growth properties and antioxidant enzymes activities of strawberry seedlings were studied by sand culture. The results indicated that the plant height, leaf area, dry matter accumulation and root/shoot ratio of strawberry seedlings in T1, T2 and T3 were significantly decreased compared to the control (CK) after 15 days of treatment. The plant heights in T1, T2 and T3 decreased by 16.1%, 36.8% and 43.9%, and the areas of functional leaf decreased by 19.7%, 34.3% and 47.5% respectively, compared to the control. With the increasing NO3- concentration, the malondialdehyde (MDA), proline, soluble protein content and relative electronic leakage of the strawberry seedlings first increased and then decreased, but all those parameters in T1, T2 and T3 were higher than in the control. The activities of antioxidant enzymes, superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) in both root and leaf, and catalase (CAT) in the root first increased and then decreased, but the CAT activity in the leaf gradually decreased with the increasing NO3 concentration. In T3, the activity of SOD in both root and leaf, APX in the root were lower than in the control. In sum, the osmolytes of strawberry seedlings increased and the plants become weaker under nitrate stress, and some antioxidant enzymes in strawberry seedlings increased at the low level of nitrate stress and decreased at the high level. The strawberry plants were stunted when growing under 48 mmol x L(-1) NO(3-) condition.