Approche isotopique pour tracer la dynamique des éléments dans deux écosystèmes forestiers du plateau lorrain, développés sur des sols polycycliques

Abstract : Two forest ecosystems in Lorraine, France (Clermont-en-Argonne CA and Azerailles AZ) developed on polycyclic soils have a complex functioning due to the presence of two different materials within the soil profile, leading to an abrupt disruption in soil texture. Indeed, they have low exchangeable Ca and Mg stocks in the silty soil upper layers (with a greater poverty in CA than in AZ), and very large stocks in deep clayey layers. These differences in upper soil fertility between the studied sites can be partly explained by a weaker aggregation in CA than in AZ (with aggregates poor in organic matter and clays). The CA soil then holds less nutrients than AZ one, despite higher atmospheric inputs and more rapid mineralization of litter. The richness of the deep soil layers in both sites, cannot be explained by the two conventional inputs i.e. atmospheric deposition and mineral weathering, A third un-expected source was identify using Sr, Ca and Mg isotopes, i.e. a mineralized groundwater table, which allows the CEC recharging of the deep clay layers by simple ion exchange when its invades the subsoil during the winter period. Trees have developed an uptake strategy into these Ca and Mg rich clay layer, to overcome the relative poverty of the upper soil layers. However the consequence of the Mg limititation of the soil upper layers in CA is visible through the increase in the internal Mg-translocation before leaf senescence.
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Léa Bedel. Approche isotopique pour tracer la dynamique des éléments dans deux écosystèmes forestiers du plateau lorrain, développés sur des sols polycycliques. Sciences agricoles. Université de Lorraine, 2015. Français. ⟨NNT : 2015LORR0074⟩. ⟨tel-01751712⟩

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