Strategies of heavy metal uptake by three plant species growing near a metal smelter

Some higher giant species have developed heavy metal tolerance strategies w hich enable them to survive and reproduce in highly metal-contaminated soil s. We have investigated such heavy metal uptake and accumulation strategies of two absolute metallophyte species (Armenia maritima ssp. halleri and Ca rdaminopsis halleri) and one pseudometallophyte (Agrostis tenuis) growing n ear a former metal smelter. Samples of plant parts and soil were analysed f or Zn, Cd, Pb, and Cu. In soil, there were two dominant types of metal conc entration gradients with depth. Under the absolute metallophytes, extremely high metal contents were measured in the surficial Ah horizon, followed by a strong decrease in the underlying soil horizons (L-11 and L-12). Under t he pseudometallophyte, metal concentrations in the Ah horizon were much low er and fewer differences were observed in metal concentrations among the Ah , L-11, and L-12 horizons. The concentrations of Zn, Cd, Pb, and Cu in Agro stis tenuis roots were greater than concentrations in leaves, indicating si gnificant metal immobilisation by the roots. For C. halleri, Zn and Cd conc entrations in leaves were > 20 000 and > 100 mg kg(-1), respectively, indic ating hyperaccumulation of these elements. Armeria maritima ssp. halleri ex hibited root concentrations of Ph and Cu that were 20 and 88 times greater, respectively, than those in green leaves, suggesting an exclusion strategy by metal immobilisation in roots. However, Zn, Cd, Pb, and Cu concentratio ns in brown leaves of Armeria maritima ssp. halleri were 3-8 times greater than in green leaves, suggesting a second strategy, i.e. detoxification mec hanism by leaf fall. (C) 2000 Elsevier Science Ltd. All rights reserved.