Formation des racines calcifiées (rhizolithes) dans les sédiments terrestres

Axe 1 - Biominéralisation

post-doctorat de Rime El Khatib

Mené du 1^er septembre 2013 au 30 juin 2015.

Laboratoires co-porteurs

• Milieux environnementaux, transferts et interactions dans les hydrosystèmes et les sols
  Porteur de projet : Arnaud Huguet
  Co-encadrante : Sylvie Derenne
• Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC)
  Co-encadrant : Sylvain Bernard

Projet de recherche

Rhizoliths are organomineral structures resulting from root and root remain preservation in secondary carbonates. The precise mechanisms of their formation remain unclear. It is generally assumed that encrustation is controlled or induced by complex organic-inorganic interactions at the plant tissue scale. The aim of our work is to carry out a multiscale and mutlitechnique characterization of natural rhizoliths at different stages of encrustation, in order to evidence the relationships existing between organic and inorganic phases and propose a general scenario for the mechanism of plant root encrustation by secondary carbonates in terrestrial sediments. Organic geochemistry tools (GC-MS, 13C solid state NMR) in addition to STXM technique were used to analyse organic matter remains, whereas SEM coupled to EDXS analyses were performed to obtain morphological and structural information at nanometric scale.

Résultats scientifiques

SEM analysis revealed the preservation of root cellular ultrastructure with remarkable integrity for all samples, suggesting that calcification has likely been promoted by intra-cellular carbonate precipitation before tissue degradation. This was confirmed by 13C NMR and STXM analyses of recent and calcified roots. Biomarker investigation showed predominance of microbial biomarkers in the former roots, in contrast with the surrounding sediment, dominated by plant biomarkers.

Plateformes techniques utilisées

• RMN de l'Institut des Matériaux de Paris Centre
• Plateforme de Microscopie électronique de l'Institut de minéralogie, de physique des matériaux et de cosmochimie
• Pole technique de géochimie organique (GC, LC) de METIS (Milieux environnementaux, transferts et interactions dans les hydrosystèmes et les sols)

Principales communications

• Étude multi-échelles et multi-techniques des mécanismes de formation des racines calcifiées dans les sédiments terrestres.
  Réunion des chercheurs francophones en géochimie organique, Chambéry
  2014
• Plant root encrustation processes: insights from a multitechnique characterization strategy
  Goldschmidt, Sacramento, Etats-Unis
  2014