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Intégration de la phénologie et de la défense mécanique dans l’espace phénotypique des plantes

Abstract : Phenology and defence are key for the evolutionary and ecological successes of plants, by affecting their growth, survival and reproduction. Surprisingly, these two aspects of plant functioning are rarely integrated into a synthetic description of plant ecological strategies. Much effort has been devoted to the description of plant resource acquisition and use, reproductive capacities and stature, but we lack knowledge about how these are connected to phenology and defence. Therefore, plant traits commonly used in comparative analyses (leaf traits, plant height, seed mass…) and functional markers of phenology and defence have been used to characterize the phenotypic space occupied by plant species found in the Mediterranean region of southern France. The work is based on two types of approaches:(a) The synthesis of trait data collected during several independent experiments conducted in different Mediterranean sites. This resulted in the constitution of one of the first dataset describing the temporal sequence of reproductive events and their covariations in a large number of species differing in life cycles, pollination and dispersal modes. We found a clear association between the temporality of these phases and the strong seasonality of climatic conditions in the Mediterranean, especially in relation to water availability, with some variations between groups of species. Correlations between traits of the reproductive phenology phases suggest that species can be distributed along a fast-slow continuum of reproductive events. We also found relationships between reproductive phenology and other traits commonly used for the description of plant phenotypes in comparative analyses: the flowering date depends on plant height, the seed maturation period affects the seed mass and the drought intensity during seed production correlates with several leaf traits.(b) An experimental approach based on a more detailed description of the plant phenotype on a restricted number of species. This dataset includes measurements of leaf production rate and describes the dynamics of flower and seed production for 23 species. We tested the level of coordination between phenological phases and revealed some rarely tested correlations between vegetative and reproductive phenology. On these 23 species, plant defence was characterized by several biomechanical properties, morphological traits and fibre content of leaves. The leaf thickness, venation network and fibre content have a significant influence on leaf mechanical properties but their relative effects depend on the biomechanical test performed. Finally, we showed that biomechanical properties could be used to understand the links between the concepts of the growth-defence trade-off and the leaf economics spectrum.This study confirms the value of using phenological and defence traits in comparative approaches, putting back these two fundamental dimensions into the broader context of plant ecological strategies.
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Jules Segrestin. Intégration de la phénologie et de la défense mécanique dans l’espace phénotypique des plantes. Biologie végétale. Université Montpellier, 2018. Français. ⟨NNT : 2018MONTG024⟩. ⟨tel-01908660⟩

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