Effects of nitrogen fertilizer on nitrogen concentration and enzyme activities in tobacco leaf in dryland and paddy field

Tobacco is mainly planted in dry land and paddy field in Yunnan.Although effects of nitrogen fertilizer on nitrogen accumulation and nitrate reductase in tobacco leaf had been extensively studied,impacts of nitrogen fertilizer on flue-cured tobacco leaf nitrogen metabolism in dry land and paddy field were not well documented.It is important to understand differences of tobacco leaf nitrogen metabolism,such as nitrogen concentration and its key enzyme activity variation during different tobacco growth stage after nitrogen treatments,in dry land and paddy field in order to improve yield and quality of tobacco leaf.In this study,the response of tobacco leaf nitrogen concentration,nitrate reductase(NR),and Glutamine synthetase(GS) to nitrogen fertilizer was investigated at five growth stages including rosette growth stage,rapid growth stage,lower stalk position leaf harvesting stage,middle stalk position leaf harvesting stage, and upper stalk position leaf harvesting stage.Split plot design with the two nitrogen forms,namely nitrate nitrogen and ammonium nitrogen,as main plots,five nitrogen levels,namely 0,37.5,75,112.5,150 kg/ha in dry land and 0, 45, 90,135,180 kg/ha severed as split plot,was adopted in the experiment.Results showed that the peak value of nitrogen concentration in tobacco leaf was always showed up at rosette growth followed by rapid growth stage.However,leaf nitrogen concentration reduced rapidly once tobacco leaf harvesting began.The NR and GS in leaf increased at rosette growth stage to rapid growth stage,and then decreased gradually in dry land and paddy field after nitrogen fertilizer application.Tobacco leaf nitrogen concentration and NR activity in paddy field was much higher than that in dry land.However,leaf GS activity in dry land was higher than that in paddy field.The result indicated that tobacco in paddy filed was able to utilize nitrogen fertilizer more efficiently,but its nitrogen assimilation ability was much weaker than that in dry land.When the nitrogen fertilization rate ranged from 0 to 75 kg/ha in dry land and 0 to 90 kg/ha in paddy field,application of nitrogen could improve leaf nitrogen concentration,NR,and GS activities.Ammonium nitrogen had greater positive effect on nitrogen uptake NR,GS,and AS activities comparing to nitrate nitrogen.