A field experiment was carried out to investigate the effects of planting density and N applica-tion on the yield , photosynthetic characteristics and enzyme activities of tobacco .The results showed that:1) Planting density and N had a positive interaction with shoot biomass;2) Planting density, N and planting density ×N had no effects on chlorophyll a ,chlorophyll b and carotenoids content .Photosynthetic rate had no difference between high and medium density , which was higher than that of low density . Under the condition of high density , the photosynthetic rate of high N was higher than that of medium and low N treatment .Under the condition of medium density , photosynthetic rate at medium N had no differ-ence compared with that at either low or high N .Photosynthetic rate at high N was higher than that at me-dium N, and photosynthetic rate at low N had no difference with that at medium or high N .Under the con-dition of low density , photosynthetic rate at high N was lower than that at low N , but photosynthetic rate at medium N had no difference compared with that at either low or high N;3) Planting density and N had a significant impact on nitrate reductase activities and amylase activities at growing and maturing stages .%采用田间裂区试验，研究3种种植密度（主处理）与3个氮水平（副处理）对烤烟产量、光合特性及代谢酶活性的影响．结果表明：1）种植密度与施氮量对地上部生长具有正交互作用．2）种植密度、施氮量、种植密度×施氮量对叶绿素a、叶绿素b和类胡萝卜素含量无显著影响．高密度与中密度处理叶片光合速率之间无显著差异，两者均显著高于低密度处理；高密度时光合速率在高氮时高于中、低氮处理；中密度时光合速率在中氮时与低、高氮时均无显著差异，高氮时显著高于中氮时；低密度时光合速率在高氮时低于低氮时，中氮处理与低、高氮处理均无显著性差异．3）种植密度与施氮量互作对旺长期和成熟期叶片硝酸还原酶活性、淀粉酶活性具有调控作用．
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