| In order to screen the combined nitrogen-fixing bacteria, which can promote barley growth, soil samples were collected from the rhizosphere of barley in different regions of Tibet. The strains were isolated on Ashby nitrogen-free medium. The fixed nitrogen content of the isolates was determined by Kjeldahl method. The germination of barley seeds and seedlings were determined by the method of culture dish paper germination. According to the strain morphology, physical and chemical characteristics, and 16S rDNA sequence analysis, nitrogen-fixing strains were identified. The results showed that 72 strains of associative nitrogen-fixing bacteria were isolated from barley rhizosphere in Tibet. The fixed nitrogen amount was between 0.30~26.07 mg·L-1, of which 10 strains had higher nitrogen-fixing amount. Compared with CK, the fixed nitrogen amount increased by 17.01~26.07 mg·L-1. The results of seed germination and seedling growth test showed that 6 of the 10 strains had better comprehensive promoting effect, namely strains 20-2, 22-5, 23-3, 26-1, 35-2 and 39-5. Compared with CK, seed germination rate increased by -7.14%~25.00%, stem diameter increased by 1.53%~13.74%, plant height increased by -9.52%~7.60%, root length increased by 9.41%~38.09%, fibrous root number increased by -11.26%~12.57%, fresh weight increased by -4.97%~57.73%. The six strains belonged to Rhizobium, Bacillus, Achrobacter and Pseudomonas. |