Root-induced changes in pH and dissolved organic matter binding capacity affect copper dynamic speciation in the rhizosphere

Bravin Matthieu, Garnier Cédric, Lenoble Véronique, Gérard Frédéric, Dudal Yves, Hinsinger Philippe. 2012. Root-induced changes in pH and dissolved organic matter binding capacity affect copper dynamic speciation in the rhizosphere. Geochimica et Cosmochimica Acta, 84 (1) : pp. 256-268.

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Abstract : Due to only few experimental evidences, the importance of root-induced alteration of metal dynamic speciation in the rhizosphere in the determination of metal bioavailability to plants is still a matter for debate. The present study thus investigated how root-induced changes in pH and dissolved organic matters (DOM) altered copper (Cu) dynamic speciation in the rhizosphere of durum wheat (Triticum turgidum durum L.). Plants were exposed to a Cu-contaminated soil previously alkalised by liming to cover soil pH values ranging from 4.8 to 7.5. A range of analytical techniques was deployed on soil exposed (i.e. in the rhizosphere) or not (i.e. in the bulk soil) to plant roots, including the measurement and the modelling (using the Humic Ion-Binding Model VI) of Cu2+ activity, the measurement of labile Cu concentration and Cu lability by Differential Pulse Anodic Stripping Voltammetry (DPASV) and Diffusive Gradients in Thin films (DGT). Due to root-induced alkalisation, pH reached about 7.3 in the rhizosphere whatever the initial bulk soil pH. Compared to the most acidic bulk soil (pH _ 4.8), Cu2+ activity decreased by three orders of magnitude in the rhizosphere while DPASV-Cu concentration decreased by 6-fold. DOM became the key driver of Cu dynamic speciation in the rhizosphere, where roots induced up to an order of magnitude increase in DOM concentration compared to bulk soils. This resulted in an increase in labile-Cu (both DPASV and DGT) concentrations, in spite of a decrease in Cu2+ activity. Model VI calculations supported a decrease in DOM binding capacity towards Cu in the rhizosphere. DPASV measurements unequivocally demonstrated that the increase in Cu lability in the rhizosphere solution can be attributed to a greater lability of organically-bound Cu. Collectively, our data introduce a consistent picture of root-induced changes of Cu dynamic speciation in the rhizosphere that were notably related to substantial alterations of DOM binding capacity. (Résumé d'auteur)

Mots-clés Agrovoc : Triticum durum, Rhizosphère, Sol pollué, Fertilité du sol, Matière organique du sol, pH du sol, Cuivre, Système racinaire

Mots-clés géographiques Agrovoc : France

Classification Agris : F62 - Plant physiology - Growth and development
P36 - Soil erosion, conservation and reclamation
P35 - Soil fertility

Champ stratégique Cirad : Axe 1 (2005-2013) - Intensification écologique

Auteurs et affiliations

  • Bravin Matthieu, CIRAD-PERSYST-UPR Recyclage et risque (FRA) ORCID: 0000-0002-1436-7837
  • Garnier Cédric, Université du Sud Toulon-Var (FRA)
  • Lenoble Véronique, Université du Sud Toulon-Var (FRA)
  • Gérard Frédéric, CIRAD-PERSYST-UMR Eco&Sols (FRA)
  • Dudal Yves, INRA (FRA)
  • Hinsinger Philippe, INRA (FRA)

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