Puschenreiter et al.(2003) investigated chemical changes in the rhizosphere of hyperaccumulators T. goesingense and T. caerulescens and the metal excluder T. arvense with a rhizosphere bag experiment on the contaminated and non-contaminated soils. Hyperaccumulation and depletion of labile Zn in the rhizosphere were observed for T. goesingense grown on the contaminated soil. In the non-contaminated soil, Zn was accumulated but labile Zn in the rhizosphere was not changed. Nickel present in background concentration in both soils was accumulated by T. goesingenseonly when grown on non-contaminated soil. In contrast, labile Ni in the rhizosphere increased in both soils, suggesting a general tendency of Ni mobilization by T. goesingense. Uneo et al.(2004a) studied the interaction between Zn and Cd in T. caerulescens in solution culture and in pot soil. Results from long term (4 weeks) and short term (1 week) solution culture experiments indicate that Cd accumulation in the shoot was not affected by the supply of a 4~10-fold excess of Zn, whereas the Cd concentration of the roots decreased with increasing Zn concentrations in the solution. The results suggest that the Ganges ecotype of T. caerulescens displayed different uptake systems for Cd and Zn and that Cd competed with Zn uptake while Zn did not compete with Cd uptake. Uneo et al.(2004b) investigated the uptake of Cd and Zn by T. caerulescens (the Ganges ecotype) from enriched soil with different insoluble and soluble sources of Cd and Zn. The data show that there was no significant differences in the shoot Cd concentration between the treatments with soluble or insoluble Cd compounds, even though Cd concentration in the soil solution was in the order of CdSO4>>CdCO3>CdS. Thlaspi caerulescens grown on the ZnS-enriched soil accumulated up to 6 900 mg Zn/kg in the shoots, although Zn accumulation was 1.5 times higher with the addition of more soluble compounds Zn3(PO4)2 or ZnSO4. These results indicate that the Ganges ecotype of T. caerulescens is able to utilize insoluble Cd and Zn compounds in soils.
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