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Rhizosphere pH gradient controls copper availability in a strongly acidic soil

Bravin M., Tentscher P., Rose J., Hinsinger P.. 2009. Environmental Science and Technology, 43 (15) : p. 5686-5691.

Using a root mat approach, we quantified how root-induced alkalization controlled the establishment of copper (Cu) gradients in the rhizosphere of durum wheat (Triticum turgidum durum L.) cropped in a strongly acidic, Cu-contaminated soil. Rhizosphere pH increased over 6 mm in soil, reaching up to+2.8 units close to root mat surface. Conversely, free Cu2+ activity decreased by 3 orders of magnitude and total Cu concentration by 3-fold in the rhizosphere solution, while labile Cu assessed by DGT (diffusive gradients in thin films) was halved. The DIFS (DGT-induced flux in soils and sediments) model failed to adequately simulate Cu depletion in the rhizosphere solution, showing that root-induced alkalization almost entirely explained Cu depletion while plant uptake had little impact. We modeled the observed pH gradient to recalculate its radial extension around a single root. The gradient of free Cu2+ activity in solution, deduced from pH modeling, extended over 1-4 mm in the rhizosphere depending on root radius and OH- efflux from root. Rhizosphere alkalization dramatically decreased root exposure to Cu, substantiating that root-induced chemical changes in the rhizosphere should be better accounted for to assess metal bioavailability to plants. (Résumé d'auteur)

Mots-clés : sol acide; sol pollué; alcalinisation; relation plante sol; ph du sol; disponibilité d'élément nutritif; rhizosphère; cuivre; triticum turgidum; france

Thématique : Chimie et physique du sol; Culture des plantes; Pollution

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