Growth, leaf nitrogen contents, and nitrate reductase activity of pear (Pyrus pyrifolia cv. Niitaka) trees as affected by different levels of nitrogen supply

摘要

The effects of different levels of nitrogen supply on growth, leaf nitrogen contents and nitrate reductase activity (NRA) were investigated in 3-year-old pear (Pyrus pyrifolia cv. Niitaka) trees grown in sand culture. The trees were supplemented with 4 different N levels (100, 200, 400, and 600 mg/litre) in the nutrient solution having ammonium and nitrate nitrogen at a rate of 1:3. Shoot growth and increase in leaf area were highest with 400 and 200 mg N/litre, respectively. Growth was greatly inhibited with 600 mg N/litre. Increasing the level of N in the nutrient solution increased nitrate nitrogen content in leaves until 90 days of treatment and then decreased, but the reverse was observed in total and reduced N. Leaf NRA was measured using anin vivo assay either with or without nitrate. Increasing N level from 100 to 200 mg/litre significantly increased both in vivo +NO3-NRA and in vivo -NO3-NRA. Further increase in the level of nitrogen supply to 400 or 600 mg/litre had no additional effect on the NRA increase. Only the in vivo -NO3-NRA significantly correlated with nitrogen concentration in the nutrient solution and with total and nitrate-nitrogen concentration in leaves. Thus, the in vivo -NO3-NRA may be useful for determining the difference in the capacity for nitrate reduction under different levels of N.