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Dynamique comparée des éléments majeurs dans les humus de forme mull dans une hêtraie du Nord-Est de la France

Abstract : Humus is the place of key tree nutrition processes. However, it remains a compartment of the ecosystem still under studied for all major nutrients and beneficial elements other than C and N. Thus, in a context of increasing pressure on forests, it matters to understand the dynamics of the elements from their input into the humus to their output towards the soil. The aims of this thesis are: (1) to identify the mechanisms and factors responsible of the major element dynamics (C, N, P, K, Ca, Mg, Mn, S, Si, Al and Fe), (2) to determine the relationships between these elements and (3) to specify the place of the humus in tree nutrition. To answer these objectives, a conceptual model based on the identification of humus inputs and outputs and the possible mechanisms present at the humus level was elaborated. The results of this thesis suggest that the element output fluxes depends on processes and reactions accelerating or delaying their release from the humus. The element release rates in the soil depend on their forms in the humus inputs (soluble, organic molecules, biominerals) and their location in the plant tissues (leaf blade vs. vein) supplying the humus. The element dynamics is also influenced by recycling reactions within the humus, such as biotic or abiotic precipitation through testate amoebae (Si, P, Ca and Mn), precipitates around hyphae (Ca, Mn, P, and K) or amorphous Si precipitates. These reactions control the mean residence times of the elements and their leaching gradient below the humus: the most soluble and least immobilized elements will be leached more rapidly and will have lower residence time. The release of these elements below the humus is another important factor that affects the availability of these elements to trees. During the growing season, when the trees upatke soil solution, less than 25% of K and P are released from humus. The ability of the soil to hold the elements produced during periods of senescence and dormancy is fundamental to ensure the sustainability of the ecosystem. In this thesis, the particles leaving the humus were quantified for the first time. In addition to their role on pedogenesis and the dynamics of C, this particle flux below the humus could increase the cation-exchange capacity of the soil and its ability to hold these leached elements during the dormant period.
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Marie Dincher. Dynamique comparée des éléments majeurs dans les humus de forme mull dans une hêtraie du Nord-Est de la France. Ecologie, Environnement. Université de Lorraine, 2020. Français. ⟨NNT : 2020LORR0170⟩. ⟨tel-03150871⟩

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