Abstract
In the current context of global changes, is mainly important to study adaptive plant strategies in response to environmental changes. Olive (Olea europaea L.), emblematic Mediterranean species, seems vulnerable to the effect of anthropogenic and climatic changes under its distribution area. The Moroccan range of wild (spontaneous) populations of this species extends along a latitudinal gradient integrated into an aridity gradient. Sampling along this gradient made it possible to study 27 populations (19 populations of sylvestris variety of the europaea subspecies, and 8 population of the endemic subspecies Olea maroccana). This thesis explores, (i) Intraspecific variability of leaf and wood anatomical traits along aridity gradient at different organization levels (interpopulation, intrapopulation and intraindividual level) (ii) the functional strategies deployed by the two wild olive subspecies interpreted as adaptive responses (iii) the relationship of these strategies with the plant communities differentiation and ecology where the studied populations were sampled. The obtained results confirm the climatic aspect of the gradient underlying this work, because they show that the main ecological factors explaining the diversity of wild olive plant communities are of climatic nature. Our results show that functional leaf traits variation of oleaster (O. e. subsp. e. var sylvestris) expresses the ability of the species to use available resources to respond to changing climatic conditions, particularly aridity. Moreover, analysis of the leaf traits intraspecific variability of the two wild olive subspecies highlights the existence of a trade-off between resources acquisition and conservation according to climate and plant community type. For wood anatomical traits, our results show a pattern of variations in response to biogeographic, climatic and vegetation gradients allowing the wild olive to maintain its sap conduction performance and consequently adapt to changes in ecological stressful conditions, in particular to aridity and aridification. The differentiation of wild olive populations along the latitudinal gradient by functional leaf and wood traits corresponds also to a differentiation of plant communities, which these populations are part of. Finally, this study has greatly expands our understanding of adaptive strategies of olive tree (Olea europaea L.) in Morocco in response to a latitudinal gradient of aridity.