ABSTRACT
The association of plant species with soils rich in various heavy metals has long been recognized (Antonovics, 1971). Examples of such distinct communities include serpentine (i.e., growing on Mg-, Ni-, Cr-, and Co-rich soils), seleniferous (i.e., growing on Se-rich soils), uraniferous (i.e., growing on U-rich soils), calamine (i.e., growing on Zn- and Cd-rich soils), and Cr/Co floras. Metal hyperaccumulator plant species are associated with these specialized metal floras, and they can concentrate metals in their above-ground tissues to levels far exceeding the concentration of metals present in the soil or in the nonaccumulating species growing nearby (Baker and Brooks, 1989). Because of their enhanced ability to accumulate metals, a recent U.S. Department of Energy (DOE) report concluded that “the genetic traits present in hyperaccumulator plants offer potential for the development of practical phytoremediation 190processes” (DOE/EM-0224, 1994). The genus Thlaspi (Brassicaceae) contains several species which can hyperaccumulate Ni. T. goesingense Hálácsy found growing on Ni-rich serpentinitic soils in Redschlag, Austria, can contain Ni at concentrations up to 15,000 μg g-1 in its shoot dry biomass (Reeves and Brooks, 1983). While the ecological role of metal hyperaccumulation is still unclear, recent evidence suggests that it may protect plants against herbivory and attack by fungal and bacterial pathogens (Boyd and Martens, 1994; Boyd et al., 1994; Pollard and Baker, 1997).
