Alleviating Phosphorus Starvation and Saline Stress in Soybean: The Role of Endophytic Streptomyces sp. M57 in Soil-Plant Microecological Regulation

Background and Aims Phosphorus (P) in saline-alkali soils is easily immobilized as insoluble phosphates, and saline stress severely restricts sustainable soybean production. Traditional physical and chemical remediation methods are inefficient and pose secondary environmental risks. This study aimed to explore the potential of endophytic Streptomyces sp. M57 in alleviating soybean P starvation and saline stress, thereby providing an efficient and eco-friendly microbial resource. Methods Strain M57 was identified via whole-genome sequencing, and its phosphate-solubilizing capacity, salt tolerance, and plant growth-promoting (PGP) traits were evaluated. The effects of M57 on soil P transformation, soybean growth, rhizosphere microbial community, and soybean gene expression were analyzed using Hedley P fractionation, pot experiments, 16S rRNA high-throughput sequencing, and transcriptomic sequencing. Results Streptomyces sp. M57 colonized soybean roots and rhizosphere soil, promoted the conversion of stable P into available P, improved soil fertility and microbial community diversity, and enriched beneficial microbial taxa. In addition, M57 enhanced the uptake and utilization of P, nitrogen (N), and iron (Fe), increased soybean biomass accumulation, strengthened tolerance to saline stress, and regulated the expression of genes involved in P transport, stress tolerance, and growth. Conclusion Streptomyces sp. M57 alleviates soybean P starvation and saline stress through multiple pathways. These results suggest that it is a promising microbial inoculant for sustainable soybean production in saline-alkali soils.