Biotransformation and bioaccumulation of selenium by arbuscular mycorrhizal fungi associated with maize roots in natural seleniferous soils

This study evaluated the role of arbuscular mycorrhizal fungi (AMF) isolated from naturally seleniferous soils in promoting plant growth, selenium (Se) uptake, and biotransformation in naturally selenium-contaminated fields. In AMF-inoculated plants, root biomass, shoot biomass, and maize cob biomass increased by 2.35-fold, 2.32-fold, and 1.93-fold, respectively, compared to control plants. Notably, AMF roots accumulated 7.80 % more selenium than control roots. However, selenium accumulation in the shoots and grains of AMF-inoculated plants was reduced by 71.83 % and 49.92 %, respectively. X-ray absorption near-edge spectroscopy revealed that toxic inorganic selenium species present in control plant roots were replaced by reduced elemental selenium in AMF-inoculated plants. Furthermore, AMF-inoculated plants exhibited higher levels of volatile organic selenium compounds, such as dimethyl selenide and dimethyldiselenide, which escaped from plant tissues, acting as a detoxification mechanism to mitigate selenium toxicity. To the best of our knowledge, this study is the first to report the role of indigenous AMF isolated from selenium-contaminated soils in facilitating selenium bioaccumulation and biotransformation to less toxic forms in plants under field conditions. The findings highlight that AMF not only enhance plant growth under selenium-stressed conditions by limiting selenium translocation to above-ground tissues but also protect plants by transforming selenium into methylated volatile derivatives. Thus, AMF protect the plants from Se toxicity by biotransformation to lesser toxic forms as well as enhancing plant growth activities. This approach can lead to successful utilization of seleniferous soils, which otherwise are considered not suitable for agricultural use.