The project will address one of the central issues in the current climatic change debate, namely the limitations of plants to adapt to a changing climate. The objective of the study is to examine the degree to which oak populations across a latitudinal gradient in America and in Europe are morphologically and physiologically differentiated, particularly in terms of tolerance to two major stresses, drought and freezing. In the first phase of the project, hosted by the laboratory of Ecology, Evolution and Behaviour of the University of Minnesota (USA), seven American oak populations sampled along a latitudinal gradient ranging from Costa Rica to North Carolina will be studied under controlled greenhouse conditions. Recreated tropical and temperate climates will allow comparison of physiological tolerances to freezing and drought among populations. Physiological and morphological responses to drought and freezing will be examined by measurement of plant hydraulic properties, including stem and leaf conductance of water and xylem vessel structure. In the second phase of the project, at the Centre d' Ecologie Fonctionnelle et Evolutive laboratory ¿ CNRS (France), southern European oak populations, which comprise an evolutionary lineage distinct from that of the American oak populations, will be investigated along a Mediterranean latitudinal gradient. The physiological tolerances of these populations to freezing and drought stress will be examined following the same procedures as used for the American oaks. This study will allow determination of whether American and European oak populations are similar in their respective anatomical and physiological adaptations. It will also increase understanding of oak species distributions and dispersion within these two geographic zones and their respective vulnerabilities to the expected climatic changes.
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