Exploring the abundance information of nifH gene and the composition and diversity of nitrogen-fixing bacterial community in the rhizosphere soil of the desert sand-fixing plant may provide basic information for enriching the microbial resource pool in desert areas. Real-time quantitative PCR and high-throughput sequencing were applied to analyze the abundance of nifH gene and the community composition of nitrogen-fixing bacteria in the rhizosphere soil of 5 shrublands of Caragana spp. growing in the desert grassland of Ningxia. The method of isolation and culture were to screen nitrogen-fixing bacteria in the rhizosphere soil of Caragana spp. and to study their diversities. The results showed that the copy number of nifH gene in the 5 rhizosphere soil samples were significantly different, the highest in Luoshan（LS）and the lowest in Shapotou（SPT）. A total of 7 phyla, 12 classes, 26 families and 30 genera of nitrogen-fixing bacteria were detected in the rhizosphere soil of Caragana spp. At the family and genus level, the community composition of nitrogen-fixing bacteria in Shapotou sample was quite different. Unclassified Proteobacteria and Phyllobacteriaceae accounted for 25.54% and 22.77%, respectively, Rhodospirillaceae accounted for 17.43%, and Mesorhizobium were dominant genus, with a relative abundance of 22.77%; the other four soil samples were dominated by Rhodospirillaceae and Skermanella, with relative abundances of 23.71%-73.45% and 23.19%-71.14%, respectively, and it accounted for the highest proportion in Luoshan sample. The isolated nitrogen-fixing bacteria belong to 15 genera, in addition to the common nitrogen-fixing groups such as Pseudomonas, Rhizobium and Enterobacter, also including Leclercia, Chryseobacterium, Stenotrophomonas, etc., the diversity is abundant.
