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Accueil du site → Doctorat → Australie → 2012 → Eucalyptus wandoo : tolerance to drought and salinity in relation to provenance and evolutionary history in southwestern Australia

University of Western Australia (2012)

Eucalyptus wandoo : tolerance to drought and salinity in relation to provenance and evolutionary history in southwestern Australia

Dalmaris, Eleftheria

Titre : Eucalyptus wandoo : tolerance to drought and salinity in relation to provenance and evolutionary history in southwestern Australia

Auteur : Dalmaris, Eleftheria

Université de soutenance : University of Western Australia

Grade : Doctor of Philosophy (PhD) 2012

Résumé
Eucalyptus wandoo Blakely is an ecologically important and widespread endemic species of Mediterranean southwestern Australia which occurs over a wide rainfall gradient (300 to 1200 mm). Large areas of its historical distribution have been cleared for agriculture, resulting in numerous environmental problems (e.g. erosion, rising water tables, secondary salinization). Over the past four decades, E. wandoo has been suffering from crown decline, which is hypothesised to be a result of environmental stress. Due to the species’ significance from a conservation perspective, and due to its potential value for the amelioration of environmental problems currently existing in the region, it is necessary to deepen our understanding of the species’ tolerance to drought and salt, two common environmental stresses in its habitat, and of the evolutionary history of the species. In order to achieve this, physiological and morphological measurements were obtained from 6-month-old seedlings exposed to drought and salinity in two large-scale glasshouse studies for 25 populations across the species’ distribution range. For comparative purposes, several populations of four co-occurring species (E. salmonophloia, E. accedens, E. capillosa and C. calophylla.) were included in both glasshouse studies. Furthermore, the chloroplast DNA variation in E. wandoo was investigated by RFLP (restriction fragment length polymorphisms), to assess the phylogeography of the species. Results showed very limited evidence of genetically determined physiological and morphological differences between populations from climatically contrasting provenances in both glasshouse experiments. Most of the variation in measured variables was found within rather than among provenances, thus minimizing the probability of identifying significant differences among populations.
In the drought experiment, the magnitude of the effect of drought was not correlated with climatic variables of the provenance location, including rainfall and Aridity Index (AI - the ratio of annual rainfall to annual potential evapotranspiration). This lack of correlation was also found for the effect of salinity, but provenances that were the least affected in terms of their shoot dry mass, and therefore the most salt-tolerant provenances, were all clustered in the south-eastern corner of E. wandoo’s distribution. The comparison of E. wandoo with four co-occuring species showed that E. wandoo physiology contrasted most with C. calophylla, a eucalypt species belonging to a different (but closely related) genus, while there were no differences with E. capillosa, one of its closest relatives. Due to relatively large plant size differences among the species, comparisons of treatment effects were partly compromised. The cpDNA analysis identified a phylogeographical structured pattern of diversity with the presence of two clades that followed a climatic gradient from the mesic to the semi-arid region of E. wandoo’s distribution. The phylogeography of E. wandoo differs from that of other studied species of the region (e.g. E. loxophleba and A. acuminata). E. wandoo appears to have a central refugial area and a more recent expansion into the northern, eastern and southern peripheral areas, indicative of a different response to historical climate change

Mots clés : Aridity index ; Eucalyptus accedens ; Mediterranean climate ; Tree species ; Local adaption ; Chloroplast DNA ; Genetic variation ; Phylogeography ; Water relations ; Climate change ; Land clearing ; Refugia ; Evolution ; Crown decline ; Eucalyptus salmonophloia ; Restricted fragment length polymorphism ; Corymbia calophylla ; Eucalyptus capillosa

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Page publiée le 16 juin 2013, mise à jour le 31 mai 2017