At varied nitrogen levels ,a pot experiment was conducted to study the effect of nitrogen on the contents of chlorophyll ,invertase ,soluble sugar ,reducing sugar and starch ,as well as the quality of the tobacco leaves for flue-curing .The results showed that the invertase and amylase activities at the mid- and late-tobacco growth stages increased with appropriate application of potassium , which also benefited the transition of nitrogen to carbon metabolism at the right time period .After 30 and 55 ds of transplantation , the contents of total soluble sugar , reducing sugar and starch in the tobacco leaves decreased with increasing potassium fertilization at the early stage of tobacco .They increased with the increased application of potassium at the mid- and late-stages after 75 ds of the transplanting ,suggesting the application of potassium would be better for carbon accumulation at the late ,not the early stage of tobacco growth .When nitrogen supply was insufficient , the growth of tobacco was slow , the photosynthetic pigments low ,and the leaf color yellowish .When excess nitrogen was present ,the tobacco grew vigorously and delayed the normal leaf-falling .Under the experimental conditions ,the optimal levels of nitrogen for the paddy field soil (available nitrogen 184.31 mg ・ kg - 1 ) ,the yellow mud field soil (available nitrogen 127.27 mg ・ kg - 1 ) , and the tidal field soil (available nitrogen 105.45 mg ・ kg - 1 ) were 0.90 g ・ pot - 1 ,1.35 - 1.90 g ・ pot - 1 ,and 1.90 g ・ pot - 1 ,respectively ,which resulted in the highest yield and the most balanced and desirable quality for the tobacco .%采用盆栽试验，研究不同供氮水平对烤烟叶片中光合色素含量及蔗糖转化酶、可溶性糖、还原糖、淀粉含量和烟叶干物质累积的影响。结果表明：施用适量氮肥提高烤烟中后期烟叶蔗糖转化酶和淀粉酶活性，促进烟叶碳代谢。在烤烟移栽后30、55 d ，烟叶可溶性糖、还原糖和淀粉含量随施氮量的增加而降低，而在烤烟移栽后75 d 随施氮量的增加而增加。说明施用氮肥有利于降低烤烟生长前期的碳积累，从而促进烤烟生长后期的碳积累。而氮素不足时，烟株生长缓慢，光合色素含量少，叶色发黄；氮素过多时，烟株生长过旺，不利于烟株叶片的正常落黄。在灰泥田（碱解氮184.31 mg ・ kg -1）、灰黄泥田（碱解氮127.27 mg ・ kg -1）、潮砂田（碱解氮105.45 mg ・ kg -1）上的最适施氮水平分别为0.90、1.35～1.90、1.90 g ・盆-1，在此条件下，烤烟产量更好，各成分也更趋于协调。
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