The speciation and distribution characteristics of Cu in Phragmites australis (Cav.) Trin ex. Steudel.

Heavy metal allocation and the mechanism(s) of metal sequestration in different clonal organs, micro-domains and subcellular structures has not been systematically studied for rhizomatous perennial plants. It is thus pertinent to investigate knowledge of the speciation and distribution characteristics of Cu in Phragmites australis to elucidating the mobility of metals in wetland plants after their uptake via root systems so as to facilitate development of strategies to enhance Cu tolerance. This study investigated the distributions of Cu in P. australis root, stem and leaf using ICP-MS, synchrotron-based X-ray micro-fluorescence and X-ray absorption spectroscopy, then evaluated the effects of Cu on cellular structure and ultrastructure via transmission electron microscopy. The results indicate a clear preferential localisation of Cu in the roots as compared with the shoots (stems and leaves). The intensity of Cu in the vascular bundles was higher than that in the surrounding epidermis and the endodermis and parenchyma outside the medullary cavity. The dominant chemical form of Cu in P. australis was similar to Cu citrate. The results suggest that although Cu can be easily transported into the vascular tissues in roots and stems via Cu citrate, most of the metal absorbed by plants is retained in the roots because if its high binding to the cell wall, thus preventing metal translocation to aerial parts of the plants. Therefore, P. australis showed a high capacity to accumulate Cu in roots, being therefore a suitable species for phytostabilisation interventions.