【目的】苗期棉花根系发育缓慢,吸收能力弱,根系吸收的氮素不能满足棉株生长发育的需要,很容易出现僵苗、弱苗。叶面施氮可以及时补充氮素营养,解决棉花苗期阶段性营养不足的问题。本研究利用15N同位素示踪技术研究喷施尿素对棉花苗期氮素吸收利用及生理生化特性的影响,以明确棉花苗期叶面喷施尿素的适宜浓度,了解其促进棉花生长发育的机理。【方法】本试验选用黄河流域常规栽培品种中棉所79为试验材料,采用随机区组设计,在棉花苗期叶面喷施0.5%、1%和2%的15N-尿素溶液,以喷清水为对照,调查了尿素不同喷施浓度棉花氮素的吸收利用及生理生化特性。【结果】1)叶面喷施15N-尿素能显著提高棉株15N含量,各施氮处理棉株内15N含量随时间的变化趋势一致,即叶面喷施后2 96 h之间,逐渐升高,96 h达到最高,此后出现下降。2)棉株可以快速吸收叶面喷施的15N-尿素,各处理棉株叶面氮素平均吸收速率的变化趋势一致,因中午气孔关闭,2 4 h出现降低;4 6 h达到最大,期间急剧上升;6 8 h急剧下降,8 12 h下降也较快,12 h后缓慢下降。0 12 h平均吸收速率非常高,为0.23 0.29 mg/(g·h)。棉株对于叶施氮素的吸收主要出现在喷施后12 h之内。3)15N-尿素浓度为0.5%、1%时,叶面吸收显著促进了根系氮素吸收,且根系吸收的氮很快被转运到地上部分。4)1%尿素喷施浓度内,硝酸还原酶、谷氨酰胺合成酶活性,叶绿素含量的变化趋势一致,均随尿素喷施浓度的增加而提高,在喷施浓度为1%时达到峰值,超过1%后开始下降。【结论】叶面尿素喷施浓度在0.5%2%之间均能显著提高棉株15N含量,促进棉株的氮素代谢,以1%效果最佳。棉株对于喷施氮素的吸收主要发生在喷施后0 12 h,平均吸收速率为0.23 0.29 mg/(g·h),96 h棉株中15N含量达到最高。棉花叶面施氮促进了根系对氮素的吸收。叶面施氮主要通过增强硝酸还原酶、谷氨酰胺合成酶活性,提高叶绿素含量,增加叶面积,促进叶片的光合作用,以此提高氮素利用效率,增加棉花株高和总生物量。 【Aim】 Cotton root system at seedling stage has slow development and weak absorption capacity. Nitrogen absorbed by root system can not meet the needs of cotton plant growth and development. It is easy to appear stiff seedlings and weak seedlings. Foliar application of nitrogen nitrogen nutrition can be timely, stage cotton seedling to solve the problem of inadequate nutrition. In this study, 15N isotope tracing technique was used to study the effects of spraying urea on nitrogen absorption and utilization and physiological and biochemical characteristics of cotton seedling in order to clarify the appropriate concentration of urea sprayed on the foliage of cotton seedling to understand its mechanism of promoting cotton growth and development. 【Method】 In this experiment, Zhongmiansuo 79, a conventional cultivar in the Yellow River Basin, was selected as the experimental material. Randomized block design was used to spray 15% urea solution of 0.5%, 1% and 2% As a control, the nitrogen uptake and utilization and physiological and biochemical characteristics of different concentrations of urea were investigated. 【Result】 1) Spraying 15N urea on the foliage could significantly increase the 15N content of cotton plants. The variation trend of 15N content in cotton plants was the same with time, that is, High, reached the highest 96 h, then declined. 2) The cotton plants could quickly absorb the 15N-urea sprayed on the foliage, and the change trend of the average nitrogen uptake rate was the same at all treatments. The stomatal closure resulted in a decrease at 24 h and a maximum at 46 h, Sharp rise; 68 h dropped sharply, 8 12 h dropped faster, 12 h after the slow decline. The average absorption rate at 0 12 h was very high at 0.23 0.29 mg / (g · h). Cotton plant leaves for nitrogen uptake mainly occurs within 12 h after spraying. 3) When the concentration of 15N-urea was 0.5% and 1%, foliar absorption significantly promoted the nitrogen uptake by the roots, and the nitrogen absorbed by the roots was quickly transported to above-ground parts. 4) The change trend of nitrate reductase, glutamine synthetase activity and chlorophyll content in 1% urea spraying concentration were the same, which were all increased with the increase of urea spraying concentration, and peaked at the spraying concentration of 1% After more than 1% began to decline. 【Conclusion】 Leaf urea concentration of 0.5% 2% could significantly increase the 15N content of cotton plants and promote the nitrogen metabolism of cotton plants with the best effect of 1%. The nitrogen uptake by cotton plants occurred at 0 12 h after spraying, and the average absorption rate was 0.23 0.29 mg / (g · h). The highest content of 15 N in 96 h cotton plants was obtained. Nitrogen fertilizer on cotton leaves promoted root uptake of nitrogen. Leaf nitrogen application enhances nitrogen utilization efficiency and increases plant height and total biomass of cotton by increasing nitrate reductase and glutamine synthetase activity, increasing chlorophyll content, increasing leaf area and promoting photosynthesis of leaves.