Can inoculation of native arbuscular mycorrhizal fungi from a mining area attenuate stress of Acacia mangium Willd. to excess manganese?

Purpose

Manganese (Mn) is crucial in low concentrations but can become toxic in soils and sediments, affecting plants and animals. Understanding how plants inoculated with arbuscular mycorrhizal fungi (AMF) tolerate Mn is crucial for the application of these microorganisms in the remediation of contaminated soils. Despite recognized benefits in various plant species, assessing plant-AMF interaction effectiveness in mitigating Mn toxicity is crucial for undocumented plants.

Methods

Acacia mangium Willd. plants were inoculated with an AMF native to a Mn mining area and grown in soil with increasing Mn levels (0, 200, and 400 mg kg⁻¹) to evaluate the effects of inoculation on plant growth and plant-AMF association strategies to reduce Mn toxicity.

Results

Inoculation with AMF resulted in beneficial effects, minimizing Mn toxicity and enhancing plant growth, despite reduced mycorrhizal colonization and AMF spore levels in the soil. Non-inoculated plants exposed to 400 mg kg⁻¹ of Mn exhibited significant reductions in shoot dry mass (64.9%), number of leaves (25%), and root length (24%) compared to AMF-inoculated plants. Mn concentration was higher in the roots of AMF-inoculated plants at all Mn levels, indicating a restriction in Mn transport to the shoot, thus minimizing damage and promoting plant growth. Energy-dispersive spectroscopy identified Mn, potassium, phosphorus, iron and calcium in AMF spores, suggesting their protective role against Mn phytotoxicity and adaptability of this species of microorganism under stress conditions.

Conclusion

The native AMF inoculation reduces toxicity and improves the growth of A. mangium Willd. under high levels of Mn in the soil.