Zinc accumulation by Thlaspi caerulescens from soils with different Zn availability: a pot study

The role of Zn bioavailability in soil on Zn hyperaccumulation by Thlaspi c aerulescens was investigated. Thlaspi caerulescens from Prayon, Belgium, an d Clough Wood, UK, were grown in pots containing unenriched soil (35 mug Zn g(-)1), or five treatments enriched with Zn compounds of different solubil ity (ZnS, Zn-3(PO4)(2), ZnO, ZnCO3, and ZnSO7. 7H(2)O). The Zn-enriched tre atments had similar total Zn contents (1000 mug Zn g(-)1), but differed gre atly in their concentrations of extractable-Zn. In the treatments with litt le extractable-Zn (unenriched and ZnS-enriched) T. caerulescens accessed Zn fractions that were not initially soluble; the mass of Zn accumulated in t he shoots on Day 90 was greater than the mass of ammonium nitrate extractab le-Zn in the soil on Day 0. Moreover, the decrease in ammonium nitrate extr actable-Zn in the unenriched treatment after growth accounted for only 50 a nd 24% of the Zn accumulated by plants of the Clough Wood and Prayon popula tions, respectively. Despite accumulation of Zn from the previously non-lab ile fraction in soil, Zn hyperaccumulation from the unenriched and ZnS-enri ched treatments was less than from the four treatments with highly extracta ble-Zn. The mechanisms involved in the solubilization of Zn were therefore not strong. The dissolution of Zn in the soil might have resulted from the very high root density in the pots either enhancing weak mobilization mecha nisms, and/or highly efficient uptake in to the roots coupled with replenis hment of the Zn taken up through the soil buffering capacity.