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Theses

Importance des traits clonaux dans la réponse à la défoliation et au pâturage chez des plantes herbacées.

Abstract : Clonality in plant corresponds to vegetative multiplication. A clonal individual is composed of genetically identical and potentially autonomous descendents (ramets), generally linked altogether by connective stems. Clonal integration confers on plants singular properties, the main ones being the ability to colonize space through diverse clonal architectures, resource storage and resource sharing between ramets. Clonal plants are dominant in the vegetation of grazed meadows. The objective of this thesis is to test the hypothesis that grazing should promote clonal traits conferring on plants resistance capacities, notably to grazing-induced defoliation (i.e. losses of above-ground tissues). This hypothesis was tested through a pluri-disciplinary approach, combining community ecology, ecophysiology and modelling. In situ vegetation sampling carried out in natural prairies, demonstrated that grazing induced defoliation is homogeneous at the scale of the clonal fragment (less than one meter) and acts as a filter on clonal traits. The combined investigation of specific composition and clonal traits, documented from databases or monitored experimentally, suggests that grazing promotes stoloniferous and caespitose growth forms, while rhizomatous growth forms dominate under ungrazed conditions. Moreover, costs associated to homogeneous defoliation decrease the investment in clonal propagation. However, architectural plasticity in response to experimental defoliation depends on species-specific structural constraints. Consequently, no convergence towards a single architecture was observed. On the contrary, a diversity of clonal architecture is likely to express in grazed meadows. Furthermore, although grazing disfavours belowground storage organs (rhizomes), carbon reserve making in the basis of ramet stems seems involved in grazing resistance. According to the results of numerical simulations, optimal clonal growth forms in the absence of defoliation and under homogeneous defoliation are similar. They tend to produce aggregated ramet networks. By contrast, heterogeneous defoliation is likely to promote the spatial dispersion of ramets. Grazing appears to favour clonal growth forms that enable to maximize spatial occupation and storage of resources, which can be mobilized readily after defoliation, while limiting the investment in costly clonal structures.
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Submitted on : Thursday, April 15, 2010 - 3:59:57 PM
Last modification on : Thursday, January 14, 2021 - 11:49:23 AM
Long-term archiving on: : Tuesday, September 14, 2010 - 6:46:17 PM

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  • HAL Id : tel-00473549, version 1

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Marie-Lise Benot. Importance des traits clonaux dans la réponse à la défoliation et au pâturage chez des plantes herbacées.. Ecologie, Environnement. Université Rennes 1, 2010. Français. ⟨tel-00473549⟩

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