非共生固氮菌及其固氮作用

生物固氮作用是生态系统中重要的氮素来源，参与固氮作用的微生物对植物的生长发育至关重要。与共生固氮微生物相比，非共生固氮微生物地域分布更广泛、种类更多，对全球生态系统中氮素循环有着重要意义。本文总结了非共生固氮菌的分类及系统发育，非共生固氮菌的群落构建过程和机制；归纳了不同生态系统(如草原、森林、海洋、农田等)、植物不同部位(如林冠、叶际、根际、根内、凋落物等)和土壤中非共生固氮菌的群落组成及固氮潜力的差异，以及影响非共生固氮菌群落组成和固氮潜力的主要因素(如气候因素、土壤理化性质、人为措施等)；并整理了常用的研究非共生固氮菌及其固氮潜力的检测方法。

Asymbiotic nitrogen-fixing bacteria and their nitrogen fixation potential

Biological nitrogen fixation is an important N source to ecosystems, and nitrogen-fixing microorganisms play important roles in plant growth and development. Compared with symbiotic nitrogen-fixing microorganisms, asymbiotic nitrogen-fixing microorganisms are more widely distributed and more diverse, and they are of significance to the nitrogen cycle in the global ecosystem. In this review, the classification, phylogeny and community assembly of asymbiotic nitrogen-fixing bacteria were summarized. We compared the differences of asymbiotic nitrogen-fixing bacterial compositions and their nitrogen-fixing potential in different ecosystems (such as grassland, forest, ocean, farmland, etc.) and different parts of plants (such as canopy, phyllosphere, rhizosphere, endosphere, litter, etc.). The main factors affecting the community structure and nitrogen-fixing potential of asymbiotic nitrogen-fixing bacteria include climatic factors, soil properties and artificial measures. The frequently-used methods for studying asymbiotic nitrogen-fixing bacteria and their nitrogen-fixing potential were also summarized.