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Accueil du site → Doctorat → Australie → 2007 → The functional significance of leaf shape variation : morphology correlates with thermal and hydraulic properties

Australian National University (2007)

The functional significance of leaf shape variation : morphology correlates with thermal and hydraulic properties

Leigh, Andrea

Titre : The functional significance of leaf shape variation : morphology correlates with thermal and hydraulic properties

Auteur : Leigh, Andrea

Université de soutenance : Australian National University

Grade : Doctor of Philosophy (PhD) 2007

Résumé
Leaf shape varies remarkably both across and within species. The functional significance of leaf shape diversity has been a subject of interest for a long time but empirical evidence to support theory is scant. Among the theories are that leaf shape variation is associated with improved thermoregulation or water delivery to the lamina. In this thesis, I investigate the relationship between the shape of leaves and their thermal and hydraulic properties. Through experiments involving 68 Proteaceae species, I used thermal imagery to measure the temperature of leaves ranging widely in shape and size. I found that large, less-lobed or unlobed leaves cooled more quickly, had a greater range of temperatures across their surface, and a higher leaf-to-air temperature difference than small, narrow or deeply lobed leaves. The magnitude of these responses was influenced by the climatic conditions present during measurements. These results support theory suggesting that leaf dimensions influence heat convection via altering the thickness of the boundary layer. To investigate the relationship between leaf shape and water use traits, I conducted experiments on Ginkgo biloba, which has two leaf types on a single tree : long-shoot leaves and short-shoot leaves. . I measured anatomical, morphological and gas exchange traits, and hydraulic resistance on the two leaf types. I found that the small lobed long-shoot leaves had greater rates of photosynthesis, conductance and transpiration, and lower hydraulic resistance than the large un-lobed shortshoot leaves. These functional differences were accompanied by anatomical and morphological differences. Having distinct structural and functional features, the two leaf types are thus specialised to the different micro-climatic conditions they experience at different sites in the canopy. My findings show that both thermal and hydraulic traits are associated with different leaf forms while also highlighting the importance of understanding leaf structure and function in terms of the interacting influence of temperature and water.

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