Abstract:

Sand culture method was used with Malus hupehensis seedlings as tested materials, ¹⁵N isotope tracer was used to study the effects of deficient Zn,moderate Zn and excess Zn（0.5,4 and 16 μmol · L^-1 Zn²⁺）and five methods[keeping in deficient Zn（0.5 μmol · L^-1 Zn²⁺ for 30 d）treatment,Zn concentrations ranged from deficient to excess（0.5 μmol · L^-1 Zn²⁺ 15 d + 16 μmol · L^-1Zn²⁺ 15 d）,moderate stable Zn supply（4 μmol · L^-1 Zn²⁺for 30 d）treatment,Zn concentrations ranged from excess to deficient（16 μmol · L^-1 Zn²⁺ 15 d + 0.5 μmol · L^-1Zn²⁺ 15 d）and keeping in excess Zn（16 μmol · L^-1 Zn²⁺ 30 d）] on the growth,nitrogen absorption and utilization. The results of the two consecutive years of testing showed that at the 30th day after the treatment,the plant dry matter,total length and total surface area of root under moderate stable Zn supply treatment were the largest,and root activity was significantly higher than that under other treatments. Nitrate reductase（NR）activity was the highest in moderate stable zinc supply treatment during the whole treatment period. The results of ¹⁵N isotope tracer showed that the ¹⁵N absorption and ¹⁵N utilization under moderate stable zinc supply treatment were the highest,followed by keeping in excess Zn and Zn concentrations ranged from deficient to excess treatment,and the lowest value was founded in keeping in deficient Zn treatment. All these results indicated that insufficient and excessive zinc supply inhibited root growth and nitrogen assimilation,limited nitrogen absorption,and was not conducive to the growth and development of seedlings. Sustained and stable zinc supply can improve root activity and maintain nitrate reductase activity,so as to achieve efficient absorption and utilization of nitrogen,thus promoting the growth of apple rootstock seedlings.

Key words: apple, zinc level, change the concentration, nitrogen, absorption