Microbial Inoculants Enhance Plant Resilience to Heavy Metal Stress: A Global Meta-Analysis

Heavy metal contamination in agricultural soils threatens food security and ecosystem sustainability worldwide. Microbial inoculants have been widely used to alleviate heavy metal phytotoxicity, yet the factors determining their efficacy remain unclear. Here, we conducted a global meta-analysis of 774 paired observations from 70 studies to evaluate the effects of microbial inoculation on plant performance under heavy metal stress. Overall, microbial inoculation significantly increased plant biomass, with greater benefits under higher levels of metal stress. Combined bacterial and fungal inoculation consistently outperformed single inoculations, while non-mycorrhizal beneficial fungi produced the strongest positive effects among individual inoculants. Soil organic carbon and sand content were positively associated with inoculation efficacy, whereas mean annual temperature was negatively associated with inoculation efficacy. Our results demonstrate that microbial inoculation is an effective strategy for enhancing plant tolerance to heavy metal stress and that its efficacy is strongly influenced by inoculation strategy and soil properties. These findings provide a quantitative basis for optimizing microbial-assisted remediation and developing context-specific management strategies for contaminated agricultural soils.