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

[Truncated abstract] 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.