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pp.84-90
This study was conducted to anticipate nitrate reduction state in tree through measurement of nitrate reductase activity (NRA) and investigate the effect of nitrogen concentrations (100, 200, 400, and 600 mg L-1) on growth, the nitrogen content of various tissue, and NRA of pear (Pyrus pyrifolia cv. Niitaka) seedlings in sand culture. Nutrient solutions used in this experiment were adjusted to pH 6.5 and fixed the ratio of ammonium and nitrate to 1:3 and trickle-irrigated 3 times a day. Tree height and dry weight of various organs in seedlings were higher in low nitrogen concentration (100 and 200 mg L-1) than in high nitrogen concentration (400 and 600 mg L-1). The shoot growth in 600 mg L-1 was extremely poor by nitrogen over supply. Increasing the nitrogen concentration, the concentration of nitrate-N in leaves and roots were insignificantly changed but that of stems increased. The accumulation of total and reduced nitrogen in all organs with increasing concentrations of nitrogen supply were increased at 30 days after treatment but those of all organs at 60 and 90 days after treatment were highest in 600 mg L-1, whereas there were no significant changes among other nitrogen concentration. The in vivo (+NO3-) NRA of all organs did not relate to nitrogen concentration but the in vivo (-NO3-) NRA of leaves except roots increased with increasing the nitrogen concentration. Therefore, the proper nitrogen concentration to promote growth and nitrate reduction of pear tree was 200 mg L-1.
