Fungi (DSE, AMF) involved in the natural attenuation and rehabilitation of the inhospitable conditions prevailing in an abandoned Pb-, Cd-, As-polluted mine-tailing deposit

Mining releases elevated volumes of mining residues that can possess inhospitable characteristics; sometimes, they contain potentially toxic elements (PTE) that can constitute a threat to the organisms. In Mexico, several areas have been impacted by mining activities from centuries ago. The objective was to identify the dark septate and arbuscular mycorrhizal fungi associated with the roots of Reseda luteola L. and Asphodelus fistulosus L. in mining residues contaminated with PTE, and to explore the role of the fungi. The work was focused on Jal Viejo, a more than 50-year-old open pit tailing partially vegetated with some plant species. We identified 60 culturable DSE fungi from the interior of the roots of the two plants. According to a phylogenetic analysis of the ITS1–5.8S-ITS2 rDNA sequences, the DSE from both plants belonged to the genera Alternaria, Colletotrichum, Setophoma, Acrocalymma-Rhizopycnis, and Stemphylium. Two isolates (Colletotrichum and Alternaria alternata) consistently exhibited tolerance to Pb and Cd in vitro; five of the DSE fungi solubilized phosphate, even in the presence of Pb and Cd. An in-vitro study demonstrated that a Colletotrichum isolate exerted a plant-growth-promoting effect on tobacco (Nicotiana benthamiana Domin, 1929) subjected to Cd through longer root length and higher plant biomass. We also identified 10 morphotypes of AMF spores in the rhizospheric soil of A. fistulosus; there was a predominance of Glomerales, with the most abundant species being Rhizophagus intraradices. Due to their abundance, their tolerance, and/or their phosphate solubilization, the relevance is argued for and highlighted of DSE and AMF in the mitigation and the natural rehabilitation of the inhospitable conditions of the mining residues.