Objective Nitrogen-fixing and phosphate-solubilizing microbes were isolated from rhizosphere soils of high-altitude wetlands for development of a biological plant growth-promoting agent in the special geographic region.

Methods Nitrogen-fixing and phosphate-solubilizing microbes were isolated from the rhizosphere soils of plants of 10 species of different families on the wetlands. Species identification and taxonomic classification on the isolates were carried out using 16S rRNA molecular biology techniques. In pot experiments, effects of the isolates on seed germination and growth promotion of Elymus nutans and Medicago sativa were evaluated.

Results Among the isolated plant growth-promoting rhizobacteria (PGPR), 7 strains exhibited robust nitrogen fixation capability, 26 showed organic phosphorus solubilization in a range of 3.24 μg·mL⁻¹ to 12.17 μg·mL⁻¹, 18 displayed inorganic phosphorus solubilization in a range of 12.21 μg·mL⁻¹ to 79.30 μg·mL⁻¹, and 22 secreted IAA in a range of 18.07 μg·mL⁻¹ to 24.80 μg·mL⁻¹. A Bacillus genus was exceptionally high in fixing nitrogen, one Pseudomonas genus in solubilizing phosphate, and one Acinetobacter genus in producing IAA. Further screening identified two superior PGPR that significantly elevated the height and biomass of the forage grasses (P＜0.05), even though not on the root development.

Conclusion The identified PGPR, i.e., SSBL12 and ASC2, applied alone or in combination in the pot experimentation, significantly promoted the growth of E. nutans and M. sativa. They could potentially be applied as a microbial agent to restore vegetation vitality on high-altitude wetlands.