title: Iron isotope fingerprints of redox and biogeochemical cycling in the soil-water-rice plant system of a paddy field.
abstract: The iron isotope composition was used to investigate dissimilatory iron reduction (DIR) processes in an iron-rich waterlogged paddy soil, the iron uptake strategies of plants and its translocation in the different parts of the rice plant along its growth. Fe concentration and isotope composition (δ56Fe) in irrigation water, precipitates from irrigation water, soil, pore water solution at different depths under the surface water, iron plaque on rice roots, rice roots, stems, leaves and grains were measured. Over the 8.5-10cm of the vertical profiles investigated, the iron pore water concentration (0.01 to 24.3mg·l-1) and δ56Fe (-0.80 to -3.40‰) varied over a large range. The significant linear co-variation between Ln[Fe] and δ56Fe suggests an apparent Rayleigh-type behavior of the DIR processes. An average net fractionation factor between the pore water and the soil substrate of Δ56Fe≈-1.15‰ was obtained, taking the average of all the δ56Fe values weighted by the amount of Fe for each sample. These results provide a robust field study confirmation of the conceptual model of Crosby et al. (2005, 2007) for interpreting the iron isotope fractionation observed during DIR, established from a series of laboratories experiments. In addition, the strong enrichment of heavy Fe isotope measured in the root relative to the soil solution suggest that the iron uptake by roots is more likely supplied by iron from plaque and not from the plant-available iron in the pore water. Opposite to what was previously observed for plants following strategy II for iron uptake from soils, an iron isotope fractionation factor of -0.9‰ was found from the roots to the rice grains, pointing to isotope fractionation during rice plant growth. All these features highlight the insights iron isotope composition provides into the biogeochemical Fe cycling in the soil-water-rice plant systems studied in nature.
authors.affiliation: Instituto de Geociências, Universidade de Brasilia, IG/GMP-ICC Centro, 70919-970 Brasilia-DF, Brazil; Laboratoire Mixte International, LMI OCE « Observatoire des changements Environnementaux », Institut de Recherche pour le Développement/University of Brasilia, Campus Darcy Ribeiro, Brasilia, Brazil.
authors.forename: J
authors.initials: J
authors.lastname: Garnier
authors.affiliation: Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement (CEREGE), UMR CNRS 7730, AMU (Aix-Marseille Université), BP 80, 13545 Aix en Provence, France. Electronic address: garnier@unb.br.
authors.forename: J-M
authors.initials: JM
authors.lastname: Garnier
authors.affiliation: Instituto de Geociências, Universidade de Brasilia, IG/GMP-ICC Centro, 70919-970 Brasilia-DF, Brazil; Laboratoire Mixte International, LMI OCE « Observatoire des changements Environnementaux », Institut de Recherche pour le Développement/University of Brasilia, Campus Darcy Ribeiro, Brasilia, Brazil.
authors.forename: C L
authors.initials: CL
authors.lastname: Vieira
authors.affiliation: Laboratoire Geosciences Environnement Toulouse, UMR 5563 CNRS - UPS - IRD, 14, Avenue Edouard Belin, 31400 Toulouse, France.
authors.forename: A
authors.initials: A
authors.lastname: Akerman
authors.affiliation: Laboratoire Geosciences Environnement Toulouse, UMR 5563 CNRS - UPS - IRD, 14, Avenue Edouard Belin, 31400 Toulouse, France.
authors.forename: J
authors.initials: J
authors.lastname: Chmeleff
authors.affiliation: Institute of Geosciences, University of São Paulo, rua do Lago, 562, São Paulo 05508-080, Brazil.
authors.forename: R I
authors.initials: RI
authors.lastname: Ruiz
authors.affiliation: Laboratoire Geosciences Environnement Toulouse, UMR 5563 CNRS - UPS - IRD, 14, Avenue Edouard Belin, 31400 Toulouse, France.
authors.forename: F
authors.initials: F
authors.lastname: Poitrasson
keywords: Bangladesh; Dissimilatory iron reduction; Geochemistry; Iron uptake; Tracer