Arbuscular mycorrhizal fungi mitigate cadmium toxicity in plants: A global meta-analysis

Arbuscular mycorrhizal fungi (AMF) are known to alleviate cadmium (Cd) toxicity in plants; however, the conditions that maximize their efficiency remain poorly understood. While previous meta-analyses have documented general benefits of AMF in Cd-contaminated soils, none has systematically examined the interactive roles of soil pH, inoculant type, and plant biomass on Cd dynamics within the soil-plant system. Here, we present a comprehensive global meta-analysis (97 studies; >500 observations) using advanced statistical approaches, random-effects modeling, meta-regression, and structural equation modelling, to identify these key boundary conditions. AMF inoculation significantly (p < 0.0001) enhanced plant biomass, root and shoot length, and chlorophyll content, while markedly reducing shoot Cd concentration. Effects on antioxidant enzymes were variable and generally non-significant. Notably, AMF efficiency was strongly context-dependent: benefits were greater in acidic soils, and microbial consortia outperformed single-species inoculants in high-biomass plants by promoting root Cd immobilization. In contrast, total soil Cd concentration was a weak predictor of AMF effectiveness (meta-regression R² ≤ 2.03%), indicating that Cd bioavailability, largely determined by pH, is more critical than total metal load. Overall, our findings provide robust evidence that AMF symbiosis is a key bio-based strategy for mitigating Cd stress in plants. This study highlights soil pH, inoculant composition, and plant biomass as critical determinants of AMF efficiency and offers practical guidance for optimizing AMF-based phytostabilization and remediation in Cd-contaminated agroecosystems.