Pisolithus arhizus Inoculation Enhances Mercury Tolerance and Growth of Trifolium repens in Mining Soils

While mining provides critical raw materials for modern infrastructure and the energy transition, it leaves behind severe environmental damages, such as soil mercury (Hg) contamination. In the present study, we present the first study evaluating the relationship of the ectomycorrhizal fungus Pisolithus arhizus with Trifolium repens (white clover) as a novel nature-based mycoremediation strategy for mercury-stressed soils. Through a controlled 2 × 2 factorial experiment over six months, we demonstrate that P. arhizus significantly enhances both plant biomass and heavy-metal tolerance. Inoculation achieved a 9.53% reduction in soil Hg and drove a dramatic 53% increase in stem growth under Hg stress (compared to 36% in non-contaminated conditions) once the extraradicular mycelial network was established. Furthermore, we report novel soil-chemistry dynamics under Hg stress, including a 16% shift in electrical conductivity alongside unexpected increases in the available potassium (+9%) and phosphorus (+3%). These findings present first results for a novel approach of mycoremediation by incorporating P. arhizus into T. repens co-cultivation as a viable remediation strategy, prior to field-scale remediation.