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Etude structurelle et fonctionelle de la plasticité de la vulnérabilité à l'embolie chez le peuplier

Abstract : Forest vulnerability against climate change is highlighted by the forest diebacks caused by intense droughts. Trees are functioning at their limit of hydraulic failure due to a little hydraulic safety margin. Their behaviour in a context of climate change is, at least partially, linked with phenotypic variability of a key parameter in drought resistance: the xylem vulnerability to cavitation. Previous studies have shown this trait to be under phenotypic plasticity. The main objective of this thesis is to study the consequences of this plasticity in the hydraulic functioning and to identify its structural basis, which is the priority for the search of the genetic determinants for this trait.Poplar saplings were cultivated under grown in contrasted water availability or light exposure in order to induce acclimation in cavitation resistance. The measurements of several functional traits reveal that the leaf area and the cavitation resistance vary the most as response of drought. Simulations using a model (SurEau) confirm the importance of these two traits in drought response, in particular for cavitation resistance. The search of structural determinants was conducted at three levels: xylem, vessel dimensions and pit ultrastructure using several microscopy techniques (S.E.M., T.E.M., optical) and X-ray microtomography. The results show that acclimation of vulnerability to cavitation relies on changes in xylem and vessel dimensions while pit structure remains constant. X-ray microtomography reveals the importance of connectivity between vessels to improve embolism resistance. Plasticity for this trait was also observed on poplar leaves and wheat stems. This calls for research of structural determinants for the primary xylem, and more generally for herbaceous species.
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Submitted on : Tuesday, May 19, 2020 - 5:50:11 PM
Last modification on : Friday, August 28, 2020 - 3:10:23 AM


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Cédric Lemaire. Etude structurelle et fonctionelle de la plasticité de la vulnérabilité à l'embolie chez le peuplier. Biologie végétale. Université Clermont Auvergne, 2019. Français. ⟨NNT : 2019CLFAC081⟩. ⟨tel-02613009⟩



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