Analyse du fonctionnement hydrique des chênes sessile (Quercus petraea) et pédonculé (Quercus robur) en conditions naturelles ; effets des facteurs du milieu et de l'éclaircie

Abstract : This work summarizes 5 years of ecophysiologica! and edaphic measurements conducted in a 35-year-old mixted oaks stand (Qercus petraea et q. robur). Mechanisms of the water transfer and resistances are analysed in liquid (sap flow) and vapour phases (stomatal conductance), at different scales (leaf, tree, canopy) under well watered or drying conditions. Both species displayed some drought tolerance features : an early but partial stomatal closure that mantained high water potential gradients and significant rates of transpiration, a low vulnerability to cavitation and a deep rooting system. Neverlheless, pedunculate oak (Q. robur) was more sensitive to embolism compared to sessile oak (Q. petraea). Water uptake distribution among soil layers was modified whenl drought increased. Seasonal trends or predawn leaf water potential and soil water potential of the wettest rooted zone were similar. Sap flux densities exhibited a low variability among trees in the weil watered and closed stand, but this variability increased sharply after thinning or under dry conditions. Stand transpiration varied among years due to both soil water availability and leaf area index and canopy structure fluctuationls ; this result was confirmed by the analyse or the effects of thinning on stand leaf area and transpiration. Variations in circumference increments were related to transpiration, directly or by the way of back effects. Variations in canopy conductance were well correlated with global radiation and vapour pressure deficit and a strong coupling with the atmosphere was observed. A mode! for both daily and hourly transpiration was developed based on Penman-Monteith equation. Finally, a water balance model was calibrated from experimental data (phenology, throughfall, transpiration) and validated by comparison with directmesurements of soil water reserve (neutron probe).
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Nathalie Bréda. Analyse du fonctionnement hydrique des chênes sessile (Quercus petraea) et pédonculé (Quercus robur) en conditions naturelles ; effets des facteurs du milieu et de l'éclaircie. Biologie végétale. Université Henri Poincaré - Nancy 1, 1994. Français. ⟨NNT : 1994NAN10024⟩. ⟨tel-01748587⟩

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