中文摘要：

氮是限制生态系统生产力的主要元素,生物固氮是自然生态系统中氮的主要来源.生物固氮包括共生、联合和自生固氮3种类型,其中联合固氮和自生固氮统称为非共生固氮.相对于共生固氮而言,非共生固氮速率虽然较低,但其不需要与其他生物形成共生体系就可以生存并进行固氮,在时空分布上更加广泛,因此对生态系统氮循环特别是素输入具有重要贡献.本文对近年有关非共生固氮微生物的多样性、土壤和叶际固氮微生物的分布特征及影响因素等研究进展进行了综述,并在此基础上阐述了现有研究中存在的问题和发展前景.

英文摘要：

Nitrogen is the main limiting factor in the productivity of ecological system,and biological nitrogen fixation is the main nitrogen source in the natural ecosystem. Biological nitrogen fixation includes 3 types： symbiotic,associate and free-living nitrogen fixation. Associate and free-living nitrogen fixations are collectively called asymbiotic nitrogen fixation. Compared with symbiotic system,asymbiotic nitrogen fixation rate is lower,but asymbiotic nitrogen fixation microorganisms can survive and fix nitrogen without forming symbiotic structure with plants,therefore play an important role in nitrogen cycling,especially nitrogen input in ecosystems,due to their wide distribution and high adaptability to different environments. In this review,we mainly introduced the research progress of asymbiotic nitrogen fixation microorganisms in terms of diversity,distribution characteristics,the factors influencing asymbiotic nitrogen fixation efficiencies in soils and phyllosphere,and also highlighted the existing problems and future perspectives in this research field.