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Mécanismes écophysiologiques impliqués dans les interactions antagonistes entre le jeune chêne sessile (quercus petraea (Matt.) Liebl.) et la molinie bleue (Molinia caerulea (Moench) L.) : rôles des transferts d'azote, des mycorhizes et des rhizodépôts allélochimiques

Abstract : A better understanding of plant interactions would improve the management of natural and artificial forest regeneration. It is well established that Molinia (Molinia caerulea), a monopolist species of understory, has a particularly depressive effect on young sessile oak (Quercus petraea) establishment and growth. Large capacity of Molinia in water and soil nutrients uptake leads to strong competition by resources exploitation. However, it seems that other interactions are involved in the relationship between young oak and Molinia. Thus, the allelopathic properties of Molinia have been suggested, but no study has shown such an effect on oak. Inversely, young oak seems to facilitate Molinia growth. Oak-Molinia interaction thus has the singularity of being antagonistic: the Molinia inhibits oak growth while this one favors grass growth, but the mechanisms involved are not entirely known. The aim of this thesis was to analyze the functional and ecophysiological mechanisms involved in the interactions between young sessile oak and Molinia. The experiments carried out in the thesis show that (i) oak quickly transfers nitrogen to Molinia by the underground pathways (rhizodeposition of nitrogen compounds in the soil) favoring grass growth, (ii) Molinia presence in the same pot leads to a decrease in the lateral root rate and ectomycorhization rate of oak and (iii) Molinia rhizodeposes secondary metabolites different from those of oak and have an allelopathic potential. In line with current work, the thesis puts into perspective that the chemical compounds emitted by plants in the soil act as real direct or indirect signals (via the biological communities of the soil) and induce neighbors modifications in their metabolism and / or their growth.
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Marine Fernandez. Mécanismes écophysiologiques impliqués dans les interactions antagonistes entre le jeune chêne sessile (quercus petraea (Matt.) Liebl.) et la molinie bleue (Molinia caerulea (Moench) L.) : rôles des transferts d'azote, des mycorhizes et des rhizodépôts allélochimiques. Biologie végétale. Université Clermont Auvergne, 2019. Français. ⟨NNT : 2019CLFAC053⟩. ⟨tel-02513004⟩

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