Zinc isotopic fractionation in Phragmites australis in response to toxic levels of zinc

Abstract

Stable isotope signature of Zn have shown great promise in elucidating changes in uptake and translocation mechanisms of this metal in plants during environmental changes. Here we tested this potential by investigating the effect of high Zn concentrations on the isotopic fractionation patterns of Phragmites australis (Cav.) Trin. ex Steud. Plants were grown for 40 d in a nutritive solution containing 3.2 µM (sufficient) or 2 mM (toxic) Zn. The Zn isotopic composition of roots, rhizomes, shoots and leaves was analysed. Stems and leaves were sampled at different heights to evaluate the effect of long-distance transport on Zn fractionation. During Zn sufficiency, roots, rhizomes and shoots were isotopically heavy (δ66ZnJMC Lyon = 0.2¿) while the youngest leaves were isotopically light (-0.5 ¿). During Zn excess, roots were still isotopically heavier (δ66Zn = 0.5 ¿) and the rest of the plant was isotopically light (up to -0.5 ¿). The enrichment of heavy isotopes at the roots was attributed to Zn uptake mediated by transporter proteins under Zn sufficient conditions and to chelation and compartmentation in Zn excess. The isotopically lighter Zn in shoots and leaves is consistent with long distance root to shoot transport. The tolerance response of P. australis increased the range of Zn fractionation within the plant and with respect to the environment.