Screening and characterization of plant growth-promoting rhizobacteria from rhizosphere of forage species in an alpine region

This study aimed to obtain growth-promoting bacteria resources of excellent herbage in alpine regions, and then identify strain resources and provide a theoretical basis for grassland vegetation restoration and the development of microbial agents. Growth-promoting bacteria were screened from the rhizosphere of Festuca sinensis, Poa pratensis, and Roegneria purpurascens in the alpine regions. The characteristics of organic and inorganic phosphorus solubilization, nitrogen fixation, and hormone secretion of the strains were evaluated, and the superior strains were identified using molecular biology. The results showed that a total of 14 strains that could dissolve organic phosphorus were screened from the rhizosphere of the three herbage species, with the phosphorus solubilizing capacity ranging from 6.51 to 141.49 µg·mL⁻¹ and the pH of strain culture media ranged from 2.97 to 3.79. A total of 16 inorganic phosphorus solubilizing strains were identified with phosphorus solubilization capacity of 371.29～538.59 µg·mL⁻¹. A total of 22 nitrogen-fixing strains were screened with nitrogen-fixing activity 91.71～160.20 nmol·(h·mL)⁻¹ (C₂H₄) and 14 strains were found secreting plant growth hormones with secretion levels of IAA at 0.10～0.92 µg·mL⁻¹, and those of gibberellin and zeatin at 0.52～139.22 and 0.12～0.99 µg·mL⁻¹, respectively. After molecular biology identification, a total of 12 strains with comprehensive growth-promoting characteristics were screened out. The strain SPCB4 was Enterobacter huaxiensis, and the remaining 11 strains were identified as five different species of Pseudomonas. The 12 strains of plant growth-promoting rhizobacteria identified in this study exhibited multiple growth-promoting characteristics and provide strain resources and a theoretic basis for subsequent grassland vegetation restoration and development of microbial agents.