中文摘要：

为明确花铃期弱光对棉花氮素代谢的影响及其内在机理,以苏棉15和科棉1号为材料,在棉株第6~8果枝的第1~2果节开花时利用遮阴网遮阴,令透光率分别为100%、80%和60%,研究遮阴条件下棉花根系吸收能力及棉株氮素代谢相关酶活性动态变化特征。结果表明,在0~50d的遮阴期内,随透光率减弱,根系吸收能力及棉株氮素代谢相关酶活性降低;遮阴15d后氮素代谢相关酶活性变化最为显著,在透光率60%处理下,苏棉15、科棉1号根系硝酸还原酶、谷氨酰胺合酶、谷氨酸合酶、谷氨酸脱氢酶活性分别下降25.1%、53.2%、39.1%和25.5%,主茎功能叶相应酶活性分别下降50.3%、24.0%、30.4%和18.9%。根系、主茎功能叶变化程度不同,说明二者的氮素代谢机制对遮阴的反应存在一定差异：遮阴条件下根系氮素代谢能力下降的原因主要是谷氨酰胺合酶/谷氨酸合酶循环介导的氮素同化能力下降,其次为硝酸还原酶介导的氮素还原能力下降;主茎功能叶氮素代谢能力下降的原因主要是硝酸还原酶介导的氮素还原能力下降,其次为谷氨酰胺合酶/谷氨酸合酶循环介导的氮素同化能力下降。遮阴条件下棉花碳、氮代谢能力降低,最终导致棉株根系、主茎功能叶氮素含量和累积量降低,棉花单株铃数、铃重、籽棉产量亦随遮阴程度加深显著减少（P〈0.05）。

英文摘要：

Cotton is an important economic crop in China and light is a major limiting factor to yield in cotton. The objective of the experiment was to clarify the effect of low light stress on nitrogen metabolism in cotton （Gossypium hirsutum L.） plant. Cotton cultivars （Sumian 15, Kemian 1） were grew in pots, and treated with three light densities （100%, 80%, 60% of natural light） at the flowering stage in 1st-2nd fruiting node on 6-8th fruiting branches. It was sampled four times with 15-day intervals from onset to bolls open. Cotton root vigor, root absorption and activities of the nitrate reductase, glutamine synthase, glutamate synthase and glutamate dehydrogenase were analyzed. The results showed that with increase of the shading level, root vigor and root absorption decreased seriously. Both in root and function leaf, activities of the nitrogen metabolic enzymes, such as NR, GS, GOGAT were seriously inhibited at the 15th days of shade. The activities of nitrate reductase （NR）, glutamine synthase （GS）, glutamate synthase （GOGAT） and glutamate dehydrogenase （GDH） decreased by 25.1%, 53.2%, 39.1%, 25.5% in root, while 50.3%, 24.0%, 30.4%, 18.9% in function leaf. The descending of nitrogen absorption in cotton root resulted from the drop of GS/GOGAT activity firstly and the drop of NR activity secondly, but the decreasing of nitrogen metabolic ability in functional leaf induced from the drop of NR activity firstly and the drop of GS/GOGAT activity secondly. Low light could repress root vigor and root absorption. The activities of NR, GS/GOGAT were also suppressed, which resulted decrease of amino acid content, soluble protein content and nitrogen accumulation both in root and function leaf with increase of the shading level. The yield of cotton plant also decreased with the shading and the boll number was the most sensitive to shade.