Hydroponic screening for metal resistance and accumulation of cadmium and zinc in twenty clones of willows and poplars.

We screened 20 different clones of willow and poplar species in hydroponic experiments for their metal resistance and accumulation properties. Plants were exposed for 4 weeks either to single additions of (microM) 4.45 Cd or 76.5 Zn, or a metal cocktail containing the same amounts of Cd and Zn along with 7.87 Cu and 24.1 Pb. Plant biomass, metal tolerance and metal accumulation pattern in roots and leaves varied greatly between clones. The leaf:root ratio of metal concentrations was clearly underestimated compared to soil experiments. The largest metal concentrations in leaves were detected in Salix dasyclados (315 mg Cdkg(-1) d.m.) and a Salix smithiana clone (3180 mg Znkg(-1) d.m.) but these species showed low metal tolerance. In spite of smaller Cd and Zn concentrations, the metal-tolerant clones Salix matsudana, Salix fragilis-1, and Salix purpurea-1 hold promise for phytoextraction as they produced large biomass and metal contents in leaves.