Seed derived fungi modulate maize responses to Cd stress

Cadmium (Cd) contamination of agricultural soils can constrain plant growth and may pose food chain risks when Cd accumulates in edible plant tissues. Seed derived fungal isolates have been investigated as potential bioinoculants for alleviating heavy metal stress, but their isolate-specific effects across levels of Cd exposure remain insufficiently characterized. AK18 and SD64 originated from a Cd contaminated site, whereas DL57 originated from a non-contaminated site, and all three isolates were evaluated under 0, 15 and 30 mg Cd kg⁻¹. Plant growth, tissue Cd accumulation, rhizosphere Cd fractionation, chlorophyll, GSH and MDA were measured. Increasing Cd exposure was associated with reduced plant growth and chlorophyll and increased Cd accumulation and MDA. Under 30 mg Cd kg⁻¹, AK18 increased root length, shoot biomass and root biomass by 70.3%, 50.0% and 45.1%, respectively, while SD64 increased root length and shoot biomass by 37.4% and 20.3%, respectively (P < 0.05). AK18 reduced shoot Cd accumulation by 42.5%, whereas SD64 reduced root Cd concentration by 25.0%. Under Cd stress, AK18 and SD64 were associated with a shift in Cd partitioning from the exchangeable fraction (F1) toward more stable fractions (F3-F5), together with higher GSH and lower MDA levels; DL57 showed more variable responses across stress levels and measured traits. Spearman correlation and redundancy analyses identified associations among plant growth, exchangeable Cd, tissue Cd accumulation, antioxidant related responses and rhizosphere Cd partitioning. Overall, the isolates showed distinct, Cd concentration dependent effects. Because fungal identity and environmental origin were not independently replicated, the observed differences cannot be attributed specifically to environmental origin.