[Screening, identification, and growth-promoting effects of cold-tolerant phosphate-solubilizing bacteria from...

Ecological restoration of degraded alpine engineering areas faced severe challenges due to soil phospho-rus deficiency and low-temperature. Chemical phosphorus fertilizers had low efficiency and easily caused environmental risks, while conventional phosphate-solubilizing bacteria showed lower activity at low temperatures. Therefore, screening microbial resources with both cold tolerance and high-efficiency phosphate-solubilizing and growth-promoting functions was crucial for achieving green ecological restoration in alpine regions. In this study, we isolated and screened cold-tolerant phosphate-solubilizing bacteria from soils of disturbed engineering areas on the Wes-tern Sichuan Plateau. We evaluated their phosphate-solubilizing capacity and abilities to secrete organic acids, si-derophores, and indole-3-acetic acid (IAA) across a temperature gradient (6, 10, and 28 ℃), and verified their growth-promoting effects in a pot experiment. We obtained three highly efficient cold-tolerant phosphate-solubilizing strains (P-6, P-18, and P-25), which were identified as members of Pseudomonas genus. These strains maintained good phosphate-solubilizing capacity within the range of 6-28 ℃, among which strain P-25 exhibited the highest phosphorus solubilization (481.26 mg·L^-1) at 10 ℃. Mechanistic analysis revealed that the three strains activated inorganic phosphorus mainly by secreting organic acids and siderophores, and strains P-18 and P-25 could synthesize IAA. Inoculation with these strains significantly increased soil available phosphorus content and promoted the growth of Elymus nutans. The P-25 treatment performed the best, with plant phosphorus content, biomass, and plant height being increased by 109.2%, 65.2%, and 6.7%, respectively. All the three cold-tolerant phosphate-solubilizing bacteria strains possessed both high-efficiency phosphate-solubilizing and growth-promoting functions, and thus had application potential in the ecological restoration of alpine engineering sites.