Pioneer plant species and fungal root endophytes in metal-polluted tailings deposited near human populations and agricultural areas in Northern Mexico

As a consequence of industrial mining activity, high volumes of tailings are scattered around Mexico. Frequently, tailings contain heavy metals (HM) which entail threats against all organisms. The aim of this research was to identify plants and root fungal endophytes in polymetallic polluted tailings with the potential to be used in strategies of bioremediation. Four deposits of mine wastes, situated in a semi-arid region near urban and semi-urban populations, and agricultural areas, were studied. The physical and chemical characteristics of substrates, accumulation of HM in plant tissues, root colonization between arbuscular mycorrizal (AMF) and dark septate endophyte (DSE) fungi, and the identification of DSE fungi isolated from the roots of two plant species were studied. Substrates from all four sites exhibited extreme conditions: high levels in sand; low water retention; poor levels in available phosphorus and nitrogen content; and potentially toxic levels of lead (Pb), cadmium (Cd), and zinc (Zn). The native plants Lupinus campestris, Tagetes lunulata, and Cerdia congestiflora, as well as the exotic Cortaderia selloana and Asphodelus fistulosus, demonstrated a relevant potential role in the phytostabilization and/or phytoextraction of Pb, Cd, and Zn, according to the accumulation of metal in roots and translocation to shoots. Roots of eleven analyzed plant species were differentially co-colonized between AMF and DSE fungi; the presence of arbuscules and microsclerotia suggested an active physiological interaction. Fourteen DSE fungi were isolated from the inner area of roots of T. lunulata and Pennisetum villosum; molecular identification revealed the predominance of Alternaria and other Pleosporales. The use of native DSE fungi could reinforce the establishment of plants for biological reclamation of mine waste in semi-arid climate. Efforts are needed in order to accelerate a vegetation practice of mine wastes under study, which can reduce, in turn, their potential ecotoxicological impact on organisms, human populations, and agricultural areas.