Characteristic analysis and preliminary identification of plant growth-promoting rhizobacteria of dominant plants in alpine grassland

The low temperature tolerant plant growth-promoting rhizobacteria that can promote the growth of degraded vegetation in alpine grassland were screened and obtained. This can enrich the resource base of high quality strains found in alpine grassland. Based on the 18 strains isolated in a previous study, the method encompassing the acetylene reduction method, molybdenum antimony anti-colorimetric method, Salkowski colorimetric method and plate standoff method, respectively, nitrogen fixation, phosphorus solubilization, IAA secretion, and antagonism to phytopathogenic fungi were measured. The results showed that 14 strains of the 18 strains that screened had nitrogen fixation, phosphorus solubilization and IAA secretion, in which the nitrogen fixing enzyme activity ranged from 25.43 to 230.52 nmol·(h·mL)⁻¹. Organic phosphorus solubilization ranged from 66.90 to 115.06 µg·mL⁻¹, the inorganic phosphorus solubilization ranged from 9.22 to 380.28 µg·mL⁻¹, and the amount of IAA secretion ranged from 12.45 to 71.71 µg·mL⁻¹. Two of the strains antagonized the pathogen Gibberella acuminata with significant effect. The inhibition rates against the pathogenic fungus G. acuminata were 30.75% and 31.00%, respectively. The characteristics of the strains were compared, and six high quality PGPR strains were screened for 16S rRNA sequence comparison to determine their taxonomic status. The strains LMG2 and LMJ2 were identified as the closest relatives to Pseudomonas piscium P50^T, LMY8 as the closest relatives to Pseudomonas kairouanensis KC12^T, CND1 as the closest relatives to Pseudomonas simiae Oli^T, and strains LNA2 and LPA7 as the closest relatives to Pseudomonas neuropathica P155^T. The six low-temperature-tolerant strains screened in the study have a variety of high quality characteristics and have the potential to be applied to the vegetation restoration of alpine degraded grassland, and can provide high quality strain resources for the subsequent preparation of microbial agents for the restoration of alpine degraded grassland.