Arbuscular mycorrhizal fungi enhance maize cadmium resistance and reduce translocation: Dependence on microplastics concentration

Background The coexistence of microplastics (MPs) and heavy metals (HMs) such as cadmium (Cd) in agricultural soils represents a growing threat to crop production and food security. While arbuscular mycorrhizal fungi (AMF) are recognized for their ability to enhance plant metal tolerance, their role in mediating crop responses under combined contamination with MPs and Cd, especially across different MPs concentrations, remains largely unexplored. This study was conducted to elucidate how AMF modulate maize growth, Cd accumulation, and soil biogeochemical processes under co-contamination with polyethylene (PE) (0, 0.5% and 5% w/w) and Cd (0, 20 mg kg ^− 1 ) with or without AMF. Results The addition of 5% PE-MPs significantly aggravated Cd toxicity in maize, elevating Cd translocation to shoots by 79.6% and causing severe growth suppression. PE-MPs also modified key soil characteristics, increasing organic matter content and pH, which promoted the transformation of Cd into less bioavailable fractions yet failed to counteract its direct phytotoxic effects. Inoculation with AMF markedly alleviated these stresses. Under Cd and 5% PE-MPs co‑contamination, mycorrhizal plants showed 87.5% higher shoot biomass, 39.6% greater phosphorus uptake, and 38.5% enhanced net photosynthesis compared to non‑inoculated plants. AMF further reduced oxidative damage, promoted Cd sequestration in cell walls, decreased the biologically active Cd pool in shoots, and lowered Cd bioavailability through shifts in soil bacterial community composition, particularly by restoring the abundance of Pseudomonadota . The beneficial effects of AMF were more evident at 0.5% PE-MPs than at the 5% concentration. Conclusions This study demonstrates that AMF confer dual protection in a PE-MPs concentration-dependent manner. AMF enhance plant physiological resilience by regulating antioxidant systems and Cd subcellular distribution, while reducing Cd bioavailability by modifying soil properties, soil bacterial diversity and Cd speciation. These