Soil-plant relationships of metallophytes of the zinc-lead-copper Dugald River gossan, Queensland, Australia

Background and aims: Metallophytes are plants that can tolerate extreme metal concentrations in the soil in which they grow. The Dugald River zinc (Zn)-lead (Pb) gossan in Queensland (Australia) is one of the largest metal deposits in the world with a surface gossan formed after weathering over millions of years. It hosts a range of metallophytes which may have potential to be used in mine site rehabilitation. This study aimed to investigate the soil-plant relationships of metallophytes on the Dugald River gossan. Methods: Plant samples and associated rooting soil samples were collected across the gossan and then analysed for metal concentrations. Soil-plant metal relationships were subsequently explored to characterise the species in relation to metal uptake behaviour. Results: The metallophyte grass, Eriachne mucronata, dominated the gossan, yet there appeared to be no direct relationship between the occurrence of metallophytes and prevailing soil metal concentrations. Using transformation-based redundancy analysis (tb-RDA), two groups of metals, copper (Cu) and Zn-Cadmium (Cd), have been identified to be the primary metals driving species distribution. Crotalaria novae-hollandiae, was able to accumulate high concentrations of each of these metals in its leaves, with up to 16,200 mg Zn kg⁻¹, 545 mg Cu kg⁻¹ and 170 mg Cd kg⁻¹. Conclusions: Soil metal concentrations alone are not suitable indications for metallophyte distribution or composition in a polymetallic environment. Crotalaria novae-hollandiae can tolerate high concentrations of metals and accumulate Zn-Cu-Cd above the respective hyperaccumulation thresholds; the species can be described for the first time as a strong polymetallic indicator-type metallophyte.