Remediating heavy metal-contaminated soil through invasive alien plant-derived biochar and stinging nettle powder

Invasive alien plant species (IAPS) threaten ecosystem integrity worldwide. IAPS eradication is expensive, and their biomass is considered waste. Producing biochar from IAPS biomasses could turn waste into a resource. At the same time, this material could be used to remediate polluted soils. Also, using widespread native weeds, such as Urtica dioica (U), as an additional amendment could further improve soil remediation. In a phytoremediation experiment, we applied biochar produced from two widespread IAPS’ biomass, i.e. Ailanthus altissima (Mill.) (BA) and Solidago gigantea Aiton (BS), at different rates (2 % and 5 % w/w) together with Urtica dioica L. powder (U) (2 % w/w) in an Arsenic (As) and Lead (Pb)-contaminated soil, using Phaseolus vulgaris L. as an indicator plant species. We measured the amendment's effects on soil pore water (SPW) properties, plant and fine root development, and soil enzymatic activities. When BS was added alone, and when BA was combined with U SPW's pH and electrical conductivity (EC) increased and [Pb] diminished, which augmented plant growth and reduced Pb uptake. Combining the biochar types and U increased the soil's enzymatic activities, fine root length, biomass, and specific root length. Finally, both biochar types with U increased As mobility in SPW, leading to higher plant uptake in roots, although without translocation to aboveground organs. Our findings contribute to developing cost-effective and environmentally sustainable practices for managing polluted soil. Simultaneously, they tackle the problem of IAPS, which can be used in the future to provide guidelines for policymakers.