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Plasticité et diversité de l’efficience d’utilisation de l’eau chez deux espèces de chêne blanc d’Europe : les chênes pédonculé (Quercus robur L.) et sessile (Quercus petraea (Matt.) Liebl.) : approche descriptive de la dynamique de réponse stomatique aux changements environnementaux

Abstract : Quercus robur L. and Quercus petraea (Matt.) Liebl. are two sympatric oak species occupying distinctive ecological niches as well as presenting disparate drought tolerances. Available litterature reports the existence of stable inter-specific differences of water use efficiency (WUE) between the two species, Q. petraea displaying higher values than Q. robur. Water use efficiency can be studied at several integration scales both spatially and temporally. Based on instantaneous foliar gaz exchange, the intrinsic water use efficiency can be determined (Wi). On the other hand, water use can be characterised by measurements of the carbon isotopic composition of plant tissues (13C) or by estimation of the whole plant transpiration efficiency (TE), thus allowing a time-integrated estimate of water use. The characterisation of WUE through these different estimators allowed us to put in evidence in oak seedlings grown under controlled conditions a higher transpiration efficiency in Q. robur even though no differences were observed between the two species regarding instantaneous measurements (Wi). TE variations were mainly linked to the variations of the biomass production by the plants while Wi variations were essentially associated to the stomatal conductance. Both intra and inter specific variations of the dynamics of stomatal response to step changes of environmental factors (light, CO2, VPD) could not be clearly linked to the variations of the different WUE estimates nor their respective components. Nevertheless, drought conditions impacted the stomatal dynamics in both species towards faster stomatal responses, especially for stomatal closing. Furthermore, the main observed differences between species were linked to biomass production. Both species displayed different carbon allocation strategies, especially regarding the root compartment. Thus, Q. petraea produced a significantly more ramified and thinner root system than Q. robur. Such behaviour was accentuated under drought stress, under which Q. robur was more sensitive than Q. petraea in term of biomass production. The complexity of the relationships between water use efficiency and all of these morphological and physiological traits as well as the possible drought tolerance implications in both oak species are discussed in this PhD thesis.
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Théo Gerardin. Plasticité et diversité de l’efficience d’utilisation de l’eau chez deux espèces de chêne blanc d’Europe : les chênes pédonculé (Quercus robur L.) et sessile (Quercus petraea (Matt.) Liebl.) : approche descriptive de la dynamique de réponse stomatique aux changements environnementaux. Agronomie. Université de Lorraine, 2019. Français. ⟨NNT : 2019LORR0120⟩. ⟨tel-02460822⟩

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