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Abstract

One-year-old sun leaves of 60 species of Eucalyptus were collected in August 2005 at an arboretum in South Australia with a mean annual rainfall of 427 mm, and 14 of the same species were sampled at an arboretum in Western Australia with a mean annual rainfall of 216 mm. We determined the genetic and phenotypic variation in carbon isotope composition (delta C-13), specific leaf area (SLA) and nitrogen content per unit area of the species at each site. There were very significant (P < 0.001) differences in delta C-13 among the species at both sites. The mean delta C-13 of the 60 species at the wetter site was -27.6 parts per thousand (from -25.8 parts per thousand in Eucalyptus youngiana to -29.9 parts per thousand in Eucalyptus salicola) and of the 14 species at the drier site was -25.3 parts per thousand (from -23.7 parts per thousand in Eucalyptus ravida to -27.3 parts per thousand in Eucalyptus ewartiana). Of the 14 species common to both sites, four species had similar values of delta C-13 at the two sites despite the differences in rainfall, whereas in others the values of delta C-13 were significantly (P < 0.001) lower (more negative) at the wet than at the dry site. The SLA and nitrogen content per unit leaf area also differed significantly among the species (P < 0.001), but there was not a common relationship between delta C-13 and SEA or between delta C-13 and nitrogen content at the two sites. The strong species by environment interaction resulted from some species demonstrating phenotypic plasticity for delta C-13, while others were inherently stable across environments.