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Fonctionnement hydrique du hêtre : architecture hydraulique et sensibilité à la cavitation

Abstract : We used a high pressure flowmeter to measure the repartition of hydraulic resistances that control water fluxes within beech crowns. We observed a gradient with higher resistances in the shade-exposed branches. This gradient is strongly correlated with irradiance that branches received during their ontogenesis. Morphology (long and short twigs) and anatomy (diameter and vessel density) of branches are modulated by irradiance. Thus, we showed in shade branches that reduction in vessel diameter and the increase of the number of node increase hydraulic resistances. Hydraulic architecture is acclimated to microclimatic conditions and allows the xylem to sustain water demand and limits dysfunctioning (cavitation and embolism). When growth conditions change (water stress, changes in irradiance), we showed an early stomatal regulation able to limit strongly water fluxes, and anatomical changes inducing an acclimation to the new conditions. However, beech xylem is vulnerable to cavitation. Over the year, we observed increased of embolism following freeze-thaw cycles during winter and when a severe drought occured early in the season (1998). When vessels are embolised, hydraulic conductivity is reduced and can be restored when new ring take place in spring.
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Damien Lemoine. Fonctionnement hydrique du hêtre : architecture hydraulique et sensibilité à la cavitation. Sciences de la Terre. Université Henri Poincaré - Nancy 1, 2000. Français. ⟨NNT : 2000NAN10013⟩. ⟨tel-01747535⟩

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