Evaluating Poplar Hybrids and Companion Herbaceous Species for Phytoremediation of Riotinto Mine Soils: Survival and Trace Element Accumulation Assessment

Ecological restoration of mine dumps poses a significant global challenge. This study explores the viability of plant growth in the soils of the Riotinto mine, where high concentration of trace elements hinders vegetation establishment. Greenhouse experiments were conducted using 5 poplar hybrids (PA148, PA149, PA152, PA153 and the parental P10) and two herbaceous species, Brassica juncea L. and Lablab purpureus , grown in both contaminated and uncontaminated soils. The contaminated soil (RT) had an initial acidic pH of 3.07, which required the addition of a sugar lime amendment (SL), to reduce the availability of cationic trace elements. Poplar hybrids were grown for 3 months in both uncontaminated (C) and amended (RT + A) soils, while the herbaceous species were grown for 1 month in C, RT, and RT + A soils. Soil parameters, including pH, organic matter (OM), and both pseudototal and available trace element concentrations (extracted using 0.01 M CaCl 2 ), were analyzed. Plant biomass, trace element accumulation, and nutritional content in aerial tissues were also assessed. All poplar hybrids survived, with P152 and P153 demonstrating the highest survival rates and significant accumulation of trace elements, particularly Cd, Pb and Zn, in their leaves under RT + A soil conditions. B. juncea showed very limited growth compared to the other species, although it accumulated the highest concentration of trace elements. In contrast, L. purpureus demonstrated successful germination and growth in RT soil, showing strong tolerance to both acidity and contamination while maintaining the lowest levels of trace elements in its aerial tissues. These results highlight the importance of selecting appropriate plant species and soil amendments tailored to site-specific conditions and remediation goals.