Mitigation of heavy metal soil contamination: A novel strategy with mycorrhizal fungi and biotransformed olive residue

• Biotransformed olive residue improves metal-contaminated soils. • Native mycorrhizal fungi aid wheat growth in metal-contaminated soil. • Enhanced soil recovery with combined olive residue and mycorrhizal fungi treatment. This study investigates a novel phytoremediation approach in, employing a synergistic treatment involving arbuscular mycorrhizal fungi (AMF) and biotransformed dry olive residue (DOR) to address heavy metal (HM) contamination in soils. The research focused on soil from the Guadiamar Green Corridor area (Aznalcóllar), characterized by bar soils with residual metal pollution (Co, As, Cr, Cd, Pb, Ni, Cu, and Zn). The findings highlight a significant improvement in soil physicochemical properties following the application of DOR, including a 3-unit increase in pH (from 4 to 7), an increase in CaCO₃ content from nearly 0 to 4, and a rise in organic matter content (from 0.92 % to 1.88 %). Additionally, the activity of all four enzymatic activities studied -dehydrogenase, β-glucosidase, phosphatase, and urease- was markedly enhanced, leading to improved biological properties. These changes led to a subsequent increase in vegetative response, as reflected in a 273 % rise in biomass, a 41 % increase in stomatal conductance, and a 47 % improvement in photosystem efficiency. Although mycorrhizal inoculation provided moderate benefit, the native species, Rhizoglomus sp. (Azn), emerged as the most effective, achieving a mycorrhization percentage of 28 % and an 80 % increase in root biomass compared to other treatments when combined with DOR. This study proposes an innovative, circular economy-driven approach to address diffuse pollution sources in the studied area by recommending the use of DOR and inoculation with sp. This approach proves superior in both soil and plant systems. Additionally, employing native inoculants and agricultural by-products, the research not only contributes to the valorization of local resources but also promotes economic growth while supporting environmental conservation efforts.