Isolation of rhizobacteria from the Cenchrus fungigraminus rhizosphere and characterization of their nitrogen-fixing performance and potential role in plant growth promotion

Aims To understand the species composition, abundance and diversity of nitrogen-fixing bacteria in the Cenchrus fungigraminus rhizosphere and to screen nitrogen-fixing bacteria to study their potential role in plant growth promotion. Methods Soil were collected from 4 depths (G1, G2, G3 and G4) of the C. fungigraminus rhizosphere, and their physical and chemical properties were determined. The diversity and abundance of nitrogen-fixing bacteria and the nif H gene was analysed. Nitrogen-fixing bacteria were screened and selected to promote growth of C. fungigraminus seedlings. Results The highest diversity and abundance of nitrogen-fixing bacteria was observed in the G2 samples collected from the C. fungigraminus rhizosphere. These bacteria mainly included Proteobacteria (93.91%), Actinobacteria (0.42%), and Firmicutes (0.18%) and were significantly affected by total nitrogen, available nitrogen and soil depth. The nif H gene copy number was highest (1.56 ± 0.17 × 10 7 copies/g ) in G2. Rhizobium pusense No. 8 and No. 28 were isolated from G1 and G2, with nitrogenase activities of 145.06 ± 4.10 and 199.78 ± 7.50 U/L . The promotion experiment revealed that the plant height, root length, and leaf length of C. fungigraminus seedlings treated with both strains significantly increased by 56.79%, 76.99% and 55.71%, and the soil moisture and total nitrogen were significantly increased compared to the control ( P < 0.05). The available nitrogen, organic matter and organic carbon in soil with strain No. 28 significantly increased compared to CK. Conclusion Rhizobacteria in the C. fungigraminus rhizosphere play an important role as plant growth promoting rhizobacteria (PGPR). Two strains showed potential for the development of biological fertilizers.