杂草作为农田生态系统中除之不尽的植物，与作物存在复杂的竞争关系。项目申请者前期研究发现，土壤养分状况可以影响棉花和杂草间的竞争关系。通过调节土壤养分含量提高棉花自身的竞争能力，降低杂草的危害，这为棉田杂草的综合防控技术体系提供了新的思路和方法。在土壤养分的变化过程中，植物根系最早感应营养物质变化信号，并产生相应的生理反应。因此，本项目预以棉花生产中施用量最大的氮肥尿素和棉田主要恶性杂草牛筋草为研究对象，通过设置不同氮水平和杂草竞争强度处理，从根系构型和建成指标、根系氮代谢相关酶活性及其基因表达、同工酶谱的变化入手，从形态-酶活-基因3个层面系统阐述棉花与牛筋草竞争关系响应氮素水平变化的生理与分子机理，以期为棉田杂草综合防除体系中的氮肥运筹技术的形成提供理论依据，推动我国“减肥减药”计划的实施。

Weed is troublesome and difficult to be controlled in the farmland ecosystem and interferes with crop. We have found that the competition between cotton and weed was affected by soil mineral nutrients, and then we presumed that the competitive ability of cotton can be improved by adjusting the concentration of soil nutrients. It provides a new idea and method to control weed. Root is the original organ which captured the information of variation in nutrient availability and caused physiological response. Therefore, it is important to clarify internal mechanisms that soil mineral nutrients regulate competition between cotton and weed. In this study, we will choose goosegrass [Eleusine indica (L.) Gaertn.], the malignant weed in cotton field in China, as model weed. Different levels of urea, the largest amount of nitrogen fertilizer for cotton cultivation, were set to clarify the relationships between the changes of the root architecture, built index and the changes of nitrogen metabolism enzyme activity, gene expression and isozymogram. The physiological and molecular mechanisms of the response of competition between cotton and weed to nitrogen stress will be clarified in architecture-enzyme-gene activity levels. These findings would provide the theoretical basis to develop effective techniques to improve the competitive ability of cotton to weed.