Embolie dans les plantes : dynamique de l'invasion d'air dans des réseaux hydrauliques naturels et artificiels sous pression négative

Abstract : To assure the transport from the roots to the leaves, vascular plants create strong depressions in the sap, next to -200 bars. This depression pulls the water column contained by the tree vascular system. The water cohesion keeps the sap under liquid state. This metastable state can breaks: cavitation bubbles appear. They create an air plug inside the plant hydraulic network and impede sap flow. This phenomena called embolism could lead to the plant death by preventing the sap transport.This thesis is dedicated to the air invasion into hydraulics networks under negative pressure. First, we study the leaf embolism. We developed a new technique which allows us to record the spatial propagation of embolism in leaves hydraulic network. We show that the embolism propagates by steps from biggest veins to smallest veins.Next, in order to understand the underlying physical laws, we use two model systems. We build artificial networks in a hydrogel which mimics the sap flow characteristics. After the relaxation of the negative pressure in the network by the nucleation of a bubble, we observe surface oscillations and the slow growth of the bubble. This growth is linked to the water transport through the hydrogel and can reach a stationary regime.As we are not able to reproduce all the characteristics of the leaf network with the hydrogel, we create a computer modeling based on the Ohm analogy between hydraulics networks and electrical circuits. We reproduce the specific features of the xylem which transport the sap: the conduits are linked by pits, small valves which limit the progression of the embolism. We were able to recover the distinctiveness steps in embolism.Finally, we discuss the application of the preceding results to wood and we present some results on Pinus sylvestris.
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Diane Bienaime. Embolie dans les plantes : dynamique de l'invasion d'air dans des réseaux hydrauliques naturels et artificiels sous pression négative. Dynamique des Fluides [physics.flu-dyn]. Université Grenoble Alpes, 2016. Français. ⟨NNT : 2016GREAY056⟩. ⟨tel-01588114⟩

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