Abstract:

The two years old Fuji/Malus robusta biennial plants were selected as test materials，and potted in sand fertilized with Hoagland’s solution. The solution included five different Ni levels. After 20 days of spraying ¹⁵N-labeled urea into apple leaves，effects of Ni on absorption，transformation，and distribution of urea in the apple trees were detected，meanwhile effects of different Ni levels on nickel content，glutamine synthetase（GS）activity and superoxide dismutase（SOD）activity of leaves were analysed in the study. The results showed that，with the increase of nickel levels，the nickel content in apple leaves improved correspondingly. Under low level of nickel treatment（0.5，1.0，2.0 mg · plant^-1 NiSO₄ · 6H₂O），the GS activity and SOD activity in leaves were higher than those of the control，and the treatment with 1.0 mg/plant NiSO₄ · 6H₂O had the best effect in the study. However，the GS activity and SOD activity in leaves under high level of nickel treatment（10 mg · plant^-1 NiSO₄ · 6H₂O）were significantly lower than those of the control. The ¹⁵N-urea utilization ratio of 0.5，1.0 or 2.0 mg · plant^-1 NiSO₄ · 6H₂O treatment was significantly higher than that of the control，and the ¹⁵N use efficiency of 1.0 mg NiSO₄ · 6H₂O treatment was up to 48.74%，which was 1.71 times as many as that of the control，but the ¹⁵N use efficiency of 10 mg · plant^-1 NiSO₄ · 6H₂O treatment reduced by 38.26% compared with the control. Nickel also had obvious effect on ¹⁵N distribution ratios in apple trees. The ¹⁵N distribution ratio in roots was the highest，followed by leaves and stems in terms of 1.0 mg NiSO₄ · 6H₂O treatment. However，¹⁵N distribution to leaves was the highest of the other treatments. Overall，the results suggested that appropriate nickel level could increase the GS and SOD activities，retard senescence of apple leaves，and improve the absorption and utilization of urea，but high nickel level could result in the opposite effect on utilization of urea.

Key words: apple, nickel, 15N-urea, absorption, utilization, distribution