Abstract:

【Objective】 Efficient nitrogen-fixing bacilli were isolated, and the relationships between microbial nitrogenase activity, competition ability and inoculation effect were investigated. The influence of inoculating nitrogen-fixing bacillus on the bacterial community in crop rhizosphere was explored. 【Method】 Nitrogen-free medium was used to isolate nitrogen-fixers and heat treatment was used for the nitrogen-fixing bacilli. Nitrogenase activity was determined with acetylene reduction assay. Microbial competition ability and inoculation effect were tested with pot culture in greenhouse. Strain identification was carried out based on the morphology, physiology, biochemical test and 16S rDNA sequences analysis. 【Result】 Three strains termed as GD062, GD082 and GD282 with relative high nitrogenase activity and strong nitrogen-fixing ability were isolated, which were identified as Bacillus spp. and Paenibacillus sp. respectively. Further result showed that strain GD082 have strong competition ability, produced an inoculation effect as well as the chemical fertilizer treatment did in the natural soil. Result also indicated that no correspondence between nitrogenase activity and inoculation effect was found. Strain competition ability influences the inoculation effect. Rhizosphere bacterial community increased significantly with the inoculation of nitrogen-fixing bacilli. 【Conclusion】 It is meaningful in agricultural practice to offer crop nitrogen nutrient through inoculation of nitrogen-fixers. Selection of efficient nitrogen fixer is a complexed process. There is no correspondence between nitrogenase activity and inoculation effect. Strain competition ability influences the inoculation effect even stronger. A nitrogen-fixing bacillus GD082 with high nitrogenase activity, strong nitrogen-fixing ability and competition ability was obtained, which is possible to be further developed as an excellent strain used in the microbial fertilizer production.

Key words: biological nitrogen fixation, bacillus, strain selection, microbial fertilizer