Abstract
The metal-accumulating trees are important plants for restoring contaminated soil because of their high biomass; however, they have not been well characterized. We examine here the metal tolerance and the growth rate of willow plants, including Salix eriocarpa, S. gilgiana and S. integra, in the presence of Cd. The synchrotron radiation-based μ-X-ray fluorescence (XRF) analysis revealed the accumulation pattern of Cd at the tip of the serration in leaves, and the phellogen and/or the phelloderm under the stem surface in S. gilgiana. μ-X-ray absorption near edge structure (XANES) spectra of Cd in all the accumulation sites are close to that of Cd ion coordinated by O ligands. Although sulfur is generally considered to detoxify Cd in the herbaceous plants, the present results suggest that the chemical form of Cd was not Cd-S in all the accumulation sites. S. gilgiana is one of the candidates for phytoremediation to restore metal contaminated soils in Japan. The present work adds a novel facet to phytoremediation technology by revealing a Cd accumulation mechanism in the woody metal accumulator.
