Abstract: Two strains with higher nitrogen-fixation activities among the six strains of N₂fixers, have been isolated from the soil of Leymus chinensis rhizosphere in the grassland Inner mongolia.According to the characteristics of morphological character and physiobiochemistry of the strains, the strain A-1 belongs to the Klebsiella axytaca, the other one B-18 belongs to the Klebsiella pneumoniae subsp.pneumoniae.The two strains have higher nitrogenase activity under the condition of low pressure of oxygen.

Key words: Rhizosphere, Associative nitrogen-fixing, Nitrogen fixing activity, Rangeland Inner mongolia, Nitrogen cycle

摘要： 作者从内蒙古锡林郭勒草原优质牧草-羊草(Leymuschinensis)根际分离筛选出两株根际联合固氮菌。根据形态特征和生理生化特性,菌株A－1属催娩克雷伯氏菌(Klebsiella oxytoca),菌株B－18属肺炎克雷伯氏菌肺炎亚种(Klebsiella pneumoniaesubsp. pneumoniae)。对其进行生理生化特性、培养特性、固氮酶活性、氧浓度对固氮酶活性影响等方面的研究。结果表明,菌株均在微好氧条件下固氮活性最高,在Hill无氮培养基上30℃恒温培养,其固氮酶活性分别在18和16小时左右达到最高峰。

关键词: 根际, 联合固氮菌, 固氮酶活性, 内蒙古草原, 氮循环