豆科作物与禾本科作物轮作是世界粮食主产国保障粮食安全，提高资源利用效率，减少化肥依赖的重要途径。根际沉积N是豆禾轮作N效应的养分基础，根际沉积N的大小既反映轮作N效应的大小，又与氮循环微生物多样性与功能基因表达密切相关。在“豆科与禾本科间混作根际C、N沉积效应及其对根际微生物多样性的作用机制”工作的基础上，本研究应用15N茎秆饲喂双标记同位素示踪分析技术和变性梯度凝胶电泳技术（DGGE），结合RT-PCR（反转录与cDNA聚合酶链式扩增相结合）技术、DNA-SIP（稳定性同位素核酸探针）与Q-PCR（实时定量PCR）技术研究根际沉积N在豆科作物与禾本科作物轮作系统运转与分配，豆科作物与禾本科作物轮作对氮循环微生物多样性与活性的影响。明确根际沉积N在豆科作物与禾本科作物轮作系统中作用，研究结果为挖掘生物固氮潜力、提高氮素利用效率、建立环境友好型的氮素利用体系提供理论与技术支撑。

Legume-gramineae rotation system offers world’s major grain-producing countries a practical way to solve food security issues, improving the efficiency of resource use and increase crop yield while reducing the synthetic nitrogen fertilizer. Rhizodeposition N of legumes plays a foundational role in N effect in legume-gramineae rotation system. To be specific, it not only determine the magnitude of N effects, but also is closely related to nitrogen-fixing microorganism dynamic and the expression of nitrogen fixation functional genes. Base on the previous work of NSFC project,the techniques of 15N labeling are applied to interpret the transportion and distribution of rhizodeposition N among soil, plant, and microbiology in the legume-gramineae rotation system. Similarly, the diversity and activity of nitrogen-fixing bacteria of the rotation system can be investigated by utilizing the techniques of denaturing gradient gel electrophoresis (DGGE) analysis, reverse transcription and polymerase chain reaction (RT-PCR), DNA-based stable isotope probing，and quantitative PCR (Q-PCR).This research can reveal the effect of N rhizodeposition under the legume-gramineae rotation system and influnce nitrogen-fixing bacteria diversity and expression of functional genes. The results of this study are the fundemental theory applied to increase produciton and ecological benefit in legume-gramineae rotation system.Furthermore, it can serve as theoretical direction and technology support to mine the potential ability of biological nitrogen fixation and establish an environmental friendly N utilization system