中文摘要：

以棉纤维比强度高（科棉1号，平均比强度为35cNtex一）和中等（美棉33B，平均比强度为32cN tex^-1）的2个基因型为材料，于2005年在江苏省农业科学院（长江流域下游棉区）和江苏省邳州县宿羊山镇（黄河流域黄淮棉区）设置氮素水平（零氮为0kghm^-2，适氮为240kghm^-2，高氮为480kghm^-2）试验，研究氮素调控棉纤维蔗糖代谢及纤维比强度的生理机制。结果表明，棉铃对位叶氮浓度随铃龄变化的趋势符合幂函数曲线【YN=at^-b，YN为棉铃对位叶氮浓度（％），t为铃龄（d），a、b为参数】。高氮水平下的a值显著增加，导致铃龄24d前纤维中蔗糖代谢相关酶（蔗糖酶、蔗糖合成酶和磷酸蔗糖合成酶）活性和蔗糖转化量、纤维素最大累积速率以及铃龄24d纤维比强度降低；零氮水平下的b值显著增加，与铃龄24d后纤维蔗糖代谢相关酶活性和蔗糖含量峰值降低、纤维素快速累积持续期缩短以及铃龄24d后纤维比强度增幅减小的关系密切。上述变化特征在品种间一致，是棉纤维发育对棉铃对位叶氮浓度做出的重要生理响应，进而导致高氮、零氮水平下的成熟纤维比强度显著降低。铃龄24d是氮素调控棉纤维蔗糖代谢及纤维比强度的转折期，该时期的棉铃对位叶氮浓度分别为3．15％（南京）和2．75％（徐州）时有利于高强纤维的形成。

英文摘要：

Fiber strength is one of the important criteria of cotton （Gossypium hirsutum L.） quality. Two cotton cultivars （KC-1, average fiber strength is 35 cN tex^-1; AC-33B, average fiber strength is 32 cN tex^-1） were used, with three nitrogen application rates （0, 240, 480 kg ha^-1）, standing for low, moderate and high nitrogen levels respectively in field experiments in Nanjing （118°50′E, 32°02′N, middle lower reaches of Yangtze River Valley） and Xuzhou （117°11′E, 34°15＇N, Yellow River Valley）, Jiangsu province, which stand for the different ecological conditions, Tile results showed that the changes of nitrogen concentration in the subtending leaf of cotton boll followed the equation： YN = at^-b [YN is nitrogen concentration in the subtending leaf of cotton boll （%）; t is boll age （d）; a and b are the parameters]. ＂a＂ was significantly high under high-nitrogen level, which, to a great extent, led to the decreases of sucrose inversion amount and activity of the enzymes （invertase, sucrose synthetase, and phosphate sucrose synthetase） before the 24th day post anthesis （DPA）, as well as the maximal speed of cellulose accumulation in cotton fiber and fiber strength at the 24th DPA. ＂b＂ was significantly high under low-nitrogen level, which made negative effects on sucrose metabolism after the 24th DPA, shorten the duration for cellulose rapid accumulation in cotton fiber and reduced the increment of fiber strength from the 24th DPA to boll opening. The changes under high or low-nitrogen levels described above were important physiological responses of cotton fiber development to nitrogen concentration in the subtending leaf of cotton boll, and ultimately resulted in lower final fiber strength, and the changes showed similar trends in KC-1 and AC-33B. The results indicated that, in the subtending leaf of cotton boll, the 24th DPA was a transition point of sucrose metabolism in cotton fiber and fiber strength regulated by nitrogen.