Variations of cadmium tolerance and accumulation among 39 Salix clones: implications for phytoextraction

Willows (Salix spp.) show large remediation potential for cadmium (Cd)-contaminated sites, with Cd phytoextraction capacity significantly varying among specie and clone levels. In this study, a relatively large number of willow clones (39 clones) from China were evaluated for the differences in Cd tolerance and accumulation exposed to 10 μM CdCl2 by hydroponic system for 35 days. The clones showed a wide variation of biomass accumulation ranging from growth inhibition to stimulation. Shoot tolerance indexes (TIs) varied between 0.09 and 1.85, and root TIs varied between 0.27 and 1.99 among clones. The large differences in Cd concentration (μg g−1 dry weight, DW) ranged from 64.7 to 663.7 in leaves, from 118.0 to 308.4 in stems, and from 163.9 to 1,426.4 in roots among clones. Leaf translocation factors (TFs) differed from 0.09 to 1.72 and shoot TFs differed from 0.15 to 1.08. Total Cd content of shoots (including leaves and stems) varied between 29.8 and 2,726.52 μg plant−1 DW among clones. With respect to TIs, TFs, Cd concentration, and shoot Cd content, the five clones showed higher Cd phytoextraction potential than the other clones. The results support that the selection of willows with enhanced phytoremediation efficiency should be concentrated on the clone level.