Chemical and biological properties in the rhizosphere of Lupinus albus alter soil heavy metal fractionation.

To understand better the suitability of white lupin (Lupinus albus L.) for phytoremediation of heavy metal-contaminated soils, the effect of its roots on chemical and biological properties of the rhizosphere affecting soil metal fractionation was studied. Plants were cultivated in two similar soils, with high levels of Zn, Cd, Cu and Pb but differing pH values (4.2 and 6.8). In the rhizosphere of both soils, its roots induced increases in water-soluble carbon, which influenced the fractionation of heavy metals and ultimately their uptake by plant roots. In the rhizosphere of the acid soil, the concentrations of 0.1M CaCl(2)-extractable Mn, Zn and Cu were lower than in the bulk soil, possibly due to their increased retention on Fe (III) hydroxides/oxyhydroxides, while in the neutral soil only the Zn concentration was lower. Higher concentrations of heavy metals were found in plants growing on the acid soil, reflecting their greater availability in this soil. The restricted transfer of heavy metals to the shoot confirms the potential role of this species in the initial phytoimmobilisation of heavy metals, particularly in neutral-alkaline soils.