Screening of Plant Growth-Promoting Rhizobacteria and their Growth-Promoting Activities for Stipa Purpurea in Alpine Grassland

Stipa purpurea is one of the dominant grass species in alpine grassland and plays a crucial role in safeguarding the ecosystem and restoring degraded grassland. To enhance the population dominance of S. purpurea and effectively prevent further grassland degradation. In this study, we screened high-efficiency plant growth-promoting rhizobacteria (PGPR) from rhizosphere soil samples, with the aim of improving the growth activity of S. purpurea through spraying PGPR. We selected functional medium for the isolation of PGPR from the rhizosphere soils of five distinct sampling sites in the alpine grasslands surrounding Qinghai Lake. Nitrogenase activity, phosphorus-solubilization, carbon-fixation, indole acetic acid (IAA)-like compounds production, and 1-aminocyclopropane-1-carboxylate deaminase production were used to assess the growth-promoting capability of the PGPR. Additionally, the ecological adaptability of PGPR was examined. Finally, the growth promotion effect of high-efficiency PGPR on S. purpurea was determined using pot experiments. The results of this study showed that 136 strains were isolated and were categorized into 18 genera based on the 16S rRNA sequences. Among these, seven strains exhibited multiple characteristics of promoting growth, and meanwhile, strains GD-1-1, YD-2-4, GD-3-9, and HD-1-1 exhibited strong resistance to drought, cold, UV, and oxidation. The strains GD-1-1 and YD-2-4 had growth-promoting effects on the growth of S. purpurea, which significantly enhance the seed germination rate, facilitate the growth of the above-ground part of seedlings, and the formation of lateral roots. Additionally, the results of the principal component analysis indicated that the interaction effect of high-efficiency PGPRs with young roots was more beneficial than that with young sprout. The results of this study provide outstanding strain resources and a theoretical foundation for the restoration of alpine degraded grassland. The findings further provide the basis for research and development of microbial fertilizer.