Abstract: The aim of this study was to screen the rhizosphere of the dominant species in an alpine meadow (Kobresia myosuroides and Polygonum viviparum), for plant growth promoting rhizobacteria (PGPR) with excellent growth-promoting properties. The rhizosphere distribution pattern was also explored for later production and applications. We screened bacteria from root surface soil (RS), the root surface (RP), and roots (HP) by the plate coating method, then re-screened bacteria in selective media containing phosphorus (Pikovskaya medium, Mengjinna medium, nitrogen-free medium) by spot inoculation of nitrogen-fixing strains. For all strains, we determined phosphorus solubilization, nitrogenase activity, and secretion of phytohormones (indoleacetic acid, IAA; gibberellin, GA₃; trans-zeatin, t-Z). Then, strains were re-screened by molybdenum blue colorimetry, gas chromatography, and high performance liquid chromatography. The first screening step yielded 68 bacterial strains, and then the next step reduced the number to 43 nitrogen-fixing phosphatase-active PGPR strains. Among those 43 strains, 17 were able to dissolve inorganic phosphorus (phosphorus content: 9.39-94.79 μg·mL^-1); 22 were able to dissolve organic phosphorus (phosphorus content: 10.37-72.82 μg·mL^-1); 30 were able to biologically fix nitrogen [nitrogenase activity: 3.79-3193.07 nmol (C₂H₄)·h^-1·mL^-1]; 26 secreted IAA (0.24-69.98 μg·mL^-1); 32 secreted GA₃ (0.34-68.87 μg·mL^-1) and 36 secreted t-Z (0.11-47.59 μg·mL^-1). There were significantly more PGPR in the RP area than in the RS and HP areas, and more PGPR in the rhizosphere of P. viviparum than in that of K. myosuroides. The ability of PGPR to dissolve organic phosphorus was greater in the K. myosuroides rhizosphere than in the P. viviparum rhizosphere. The number of PGPR was inversely related to the ability to dissolve inorganic phosphorus in the rhizosphere. In the strains that secreted phytohormones, the most abundant was t-Z, followed by GA₃ and then IAA. The main phosphate-solubilizing strains (ZNRS2, SNRP2, ZKHP3, ZKRP1), nitrogen-fixing strains (SKRP2, SNHP1, ZNRS3), and phytohormone-producing strains (SKHP3, ZNHP2, ZKRS2, ZKRP1, ZKRP2) could be used for microbial fertilizer production and related research. The strain ZKRS2 had the strongest growth promoting effect, and should be studied in more detail.

Key words: alpine meadow, phosphate-solubilizing microorganisms, nitrogen-fixing bacteria, characteristics of dissolved phosphorus, nitrogenase activity, indoleacetic acid, gibberellin, trans-zeatin