Caractérisation expérimentale des relations entre les bactéries des sols, les phyllosilicates et les solutions : modélisation et rôle des paramètres environnementaux

Abstract : The bacteria play an important role in soil functioning and are also involved to the weathering of silicate minerals. The silicate weathering controlled the leaching of essential major mineral elements in solution, essential to maintaining soil fertility. However, although the main weathering processes of silicates are well known in aerobic (the proton- and ligand-promoted dissolution), this function of bacterial weathering of silicate minerals has never been used as a biological indicator of soil fertility. The first aim of this work was therefore to identify the process of weathering in two phyllosilicates by heterotrophic bacteria, using an empirical model of silicates weathering based on the activity of protons and ligands to identify and study the interactions between bacteria and minerals. Tracing of weathering processes by isotopic approach using stable isotopes of Mg has also been tested. The second aim was to correlate the "silicate weathering" function of bacterial communities of various soils in field conditions. This study confirms that the partial oxidation of glucose to organic acids is the predominant mechanism by which bacteria accelerate the leaching of elements under aerobic conditions during the weathering of biotite and phlogopite especially at pH close to neutrality. The empirical model used has been adapted to compare the initial release rate of iron in bacterial and abiotic weathering of micas to identify the two major processes involved. This approach highlighted the identification of phenotypes according to the metabolism and the competence of the bacterial strains used. The study with stable isotopes of Mg as tracers of weathering showed no fractionation during the proton- and ligand-promoted dissolution. Using the model in the second part of this work showed that the silicate weathering potential by microbial communities depends on their origin and in particular the contents of OM and nutrients of soil horizons sampled. Two strategies of silicate weathering in these communities have been identified: (1) the bacterial communities isolated from nutrient-rich horizons released few organic acids, but very chelating (strategy K), (2) communities isolated from nutrient-poor horizons release many low chelating organic acids (strategy r). The interdisciplinary approach proposed in this work to identify and characterize the weathering of phyllosilicates by soil heterotrophic bacteria or communities in different environments. It provides a original and promising tool for identifying functional to evaluate the quality of natural soils
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Clarisse Balland. Caractérisation expérimentale des relations entre les bactéries des sols, les phyllosilicates et les solutions : modélisation et rôle des paramètres environnementaux. Sciences agricoles. Université Henri Poincaré - Nancy 1, 2010. Français. ⟨NNT : 2010NAN10016⟩. ⟨tel-01748206⟩

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