Nanoscale chemical imaging of organo-mineral fractions of an andosol (La Martinique, France)

Miss Floriane JAMOTEAU1, Mr Nithavong CAM1, Mr Clément LEVARD1, Mr Thierry WOIGNIER2,3, Mr Romain SOULAS4,5, Mrs Isabelle BASILE-DOELSCH1

1Aix Marseille Univ, CNRS, IRD, INRA, Coll France, CEREGE, Aix-en-Provence,  France, 2Institut Méditerranéen de Biodiversité et d’Ecologie, Campus Agro Environnemental Caraïbes, Le Lamentin, France, 3Univ Avignon, CNRS, IRD, IMBE, Marseille, France, 4Univ. Grenoble Alpes, F-38000, Grenoble, France, 5CEA, LITEN,  17 Rue des Martyrs, F-38054, Grenoble, France

Organo-mineral associations are a main process driving organic matter (OM) stabilization in soils, but mechanisms of their dynamics are still not fully known. Basile-Doelsch et al. suggested that mineral alteration generating amorphous phases on minerals’s surfaces was a driver of OM stabilization. Coprecipitation synthesis led to a new model of organo-mineral associations at nanoscale, combining nanosized Co-precipitates of inorganic oLIgomers with organiCs molecules (nanoCLICs, Tamrat et al.). In the present study, we investigated nanoCLICs in soils using TEM (FEI Tecnai Osiris 200kV) coupled with 4 EDX detectors and EELS to semi-quantify C, N and major elements. We analyzed an andosol (15-20 cm) from La Martinique (French West Indies). OM-short-range-order and mineral associations were collected in the supernatant after sonication and a 48h-decantation. Areas analyzed ranged from 5 µm to 300 nm with pixel resolutions from 500 to 3 nm. Amorphous mineral phases were dominant. Fe, Si, Al and O were the main component and were homogeneous at nanoscale. Even down to 50 nm they were systematically associated to C and N. Proportions varied about 60% of Si, 30% of Al and 10% of Fe. No imogolites or allophanes were observed, mineral phases must be less polymerized (Levard et al.). Images acquired are similar to those obtained by coprecipitation on synthetic samples (Cam et al.). The nanoCLICs model (Tamrat et al.) seems to be valid in andosols. By focusing on a mg-vermiculite surrounded by amorphous material, chemical profiles showed an increasing C content from the center of the vermiculite to the amorphous material (over 150 nm). Although the amorphous phase may be bonded on mineral surface by sample preparation, these first results suggest a continuous alteration of minerals resulting in an amorphous phase progressively associated to OM molecules, as proposed by Basile-Doelsch et al.


Dr I. Basile-Doelsch. MSc in Geology (ENSG, Nancy, France), PhD in Geochemistry for paleoclimatic reconstructions (Vostok ice core, Antarctica), Habilitation à Diriger des Recherches in geochemistry of soils and weathering systems in the critical zone. She is specialized in organomineral interactions in soils. She has been an Aix-Marseille University lecturer since 1998 (France), and a junior member of the prestigious “Institut Universitaire de France” from 2011 to April 2015. As of May 2015, she became a Director of Research at the French INRA institute(CEREGE). She recently spent one year as a visiting scientist in Jeff’s Baldock group at CSIRO Adelaide.

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