Global and regional soil salinization drives bacterial diversity loss and biogeochemical imbalance

Soil salinization threatens ecosystem health, yet quantitative impacts on bacterial diversity and function remain unclear. Here we integrate a global meta-analysis with a regional field study. Salinization increased soil pH (2.9%) and bulk density (7.2%) while reducing clay content (28%). Beyond a threshold of 2.58 dS/m, bacterial Shannon diversity declined nonlinearly and richness decreased sharply. Communities shifted toward salt-tolerant Bacteroidetes (36.4% increase) and Firmicutes (34.2%), while sensitive Acidobacteria and Actinobacteria declined (95.3% and 18.3%). Random forest modeling identified sodium and magnesium ions as primary drivers. Functional gene analysis revealed nonlinear decreases in carbon, nitrogen, and phosphorus cycling genes past thresholds, but sulfur cycling genes were stimulated. Co-occurrence networks indicate environmental filtering and reduced complexity under salt stress, yet carbon metabolic functions maintain high connectivity, suggesting functional persistence among salt-adapted taxa. Collectively, salinization restructures bacterial communities via niche-based assembly ion-nutrient-physical interactions, creating microbial critical transition threshold for predicting ecosystem stimulation. Soil salinization restructures bacterial communities via biochemical changes such as elevated iron concentrations, increased pH and bulk density, and reduced clay content, based on global meta-analysis with a high-resolution regional investigation.