Soil salinization severely threatens global crop production. Understanding the relationship between crop saline–alkaline tolerance physiology and the rhizosphere microbiome, and leveraging beneficial microorganisms to enhance crop stress resistance, holds importance for sustainable agricultural development. This study investigated the physiological and rhizosphere microbial responses of two soybean cultivars with different saline–alkaline tolerance to stress. Under saline–alkaline conditions, the tolerant cultivar exhibited superior physiological performance, including higher chlorophyll content, photosynthetic efficiency, and elevated activities of antioxidant enzymes (SOD, POD, and CAT), alongside reduced oxidative damage (MDA) and greater biomass accumulation. Combined metagenomic and physiological analyses revealed significant correlations of Bradyrhizobium and Solirubrobacter with key physiological indicators, including dry weight, PI_ABS, φ_po, and MDA. The tolerant cultivar selectively enriched distinct marker microbes, such as Bradyrhizobium sp. and Bradyrhizobium liaoningense, in its rhizosphere. We conclude that the tolerant cultivar exhibits strong intrinsic physiological resistance. This resistance is further enhanced by a beneficially assembled rhizosphere microbiome, while the host plant’s physiology remains the dominant factor.

Phosphorus (P) deficiency severely limits soybean (Glycine max L.) productivity. This study proposed a three-stage screening framework to identify reliable traits and P-efficient genotypes. In Experiment I, percent tolerance to phosphorus deficiency (PTPD) was calculated for ten growth parameters across 98 genotypes under P-deficient and control conditions. Principal component analysis and comprehensive evaluation identified six key indicators in Experiment I, which were subsequently refined to five indicators through further analysis: SPAD at V3 and R1, photosynthetic rate at R1, shoot dry weight at R8, and seed number per plant at R8. Experiment II re-evaluated these traits using 12 contrasting genotypes under three P levels, identifying CN 15 as the most P-efficient and SN 22 as the most P-inefficient. Experiment III further revealed that CN 15 maintained superior PSII performance and exhibited a 26.2% increase in grain P-utilization efficiency under 0 µM KH₂PO₄ treatment. This integrated framework offers a preliminary reference for screening P-efficient soybean genotypes under controlled conditions, pending field evaluation.