Description succincte
(Anglais)
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This project aims at a better understanding of the mechanisms involved in the hyperaccumulation of metals by plants. In particular, the role of root induced mobilisation of heavy metals in this extreme uptake is investigated, and the risk involved with respect to metal mobility in the soil and finally to metal leaching to the groundwater. Such knowledge is of utmost importance when evaluating hyperaccumulating plants for the purpose of phytoremediation.
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Partenaires et organisations internationales
(Anglais)
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AT, BE, BG, CY, CZ, DK, FI, FR, DE, EL, HU, IE, IT, NL, NO, PL, SK, SI, ES, SE, CH, UK
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Résumé des résultats (Abstract)
(Anglais)
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The goal of this study was to investigate the role of organic root exudates on metal solubility and speciation in the rhizosphere of plants. For this purpose, we used a rhizobox system combined with microsuction cups to obtain direct information about the rhizosphere effect on metal speciation in soil solution. Three plants were studied: Lupinus albus as a model plant well known to exude organic acids, the hyperaccumulator Thlaspi caerules-cens and the non-hyperaccumulator Thlaspi perfoliatum. In a first step, the methodology was established by studying the exudation of low molecular weight organic acids as well as the depletion of nutrient anions in the rhizosphere of specific root segments of Lupinus albus. Clear gradients from bulk to rhizosphere soil could be detected. In addition, the temporal development of organic acid exudation during the life time of a cluster root and a diurnal cycle with maximum exudation in the afternoon were characterized. In a second step, the effect of organic acid exudation on the concentration and speciation of metals in the rhizosphere of cluster roots of Lupinus albus was investigated. For most of the metals analyzed we observed an increase of their concentrations during the exudative burst of citrate. However, for most metals this was not directly caused by citrate itself but through an indirect influence of citrate on DOC mobilization and consequently mobilization of metals by increased DOC concentrations. The comparison of metal concentrations in the rhizosphere of different Thlaspi plants and in the bulk soil indicated stronger complexation of Zn and Cd in the rhizosphere of the hyperaccumulator T. caerulescens compared to the rhizosphere of Thlaspi perfoliatum and the bulk soil. The used approach allowed to successfully follow changes in metal concentration and speciation in solution over several days or weeks without disturbance of the plant-soil system.
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