Accumulation of Heavy Metals in Conyza canadensis

Many plant species are known to take up metals from the soil and accumulate them to potentially toxic levels. This may provide tolerance to soils with high metal content or a defensive mechanism against herbivores and pathogens. Accumulators, plants that uptake and store elevated concentrations of metals, can be used in phytoremediation as a means to remove metals from contaminated soils. In this study, the native weed Conyza canadensis was grown in soils contaminated with elevated levels of lead (Pb), barium (Ba), zinc (Zn), copper (Cu), or chromium (Cr). All metals, except for Cr, were accumulated by the plants. Zinc and Cu, both essential elements, accumulated to the highest levels, while Pb and Ba were present at lower levels. All treatments except Cr showed accelerating rates of accumulation over the eight-week experiment. Barium, Cu, and Cr reduced aboveground biomass of the plants, indicating toxicity or a cost to metal accumulation. Lead and Zn promoted early flowering, while plants accumulating Ba, Cr, and Cu flowered in lower numbers. Overall, C. canadensis has promise in the phytoremediation of Pb, Cu, and Zn.