Effects of nutrient variability on the genetic-based resistance of Eucalyptus globulus to a mammalian herbivore and on plant defensive chemistry

• Published in: Oecologia 2005-02, Vol.142 (4), p.597-605
• Main Authors: O'Reilly-Wapstra, J.M, Potts, B.M, McArthur, C, Davies, N.W
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Chemistry; Environmental conditions; Environmental effects; Essential oils; Eucalyptus - chemistry; Eucalyptus - genetics; Eucalyptus - growth & development; Eucalyptus globulus; Feeding Behavior; Female; fertilizer application; Fertilizers; Foliage; Fundamental and applied biological sciences. Psychology; genetic resistance; Genetic variation; Genotype; Genotype & phenotype; Genotypes; Herbivores; Leaves; Male; Mammals; Metabolites; Nitrogen; Nutrients; pest resistance; Plant Animal Interactions; Plant biochemistry; Plant Leaves - chemistry; Plant resistance; Plants; Plants, Edible; resistance mechanisms; secondary metabolites; Seedlings; Seedlings - growth & development; Synecology; Tannins; Terrestrial ecosystems; tree nutrition; Trichosurus; Trichosurus vulpecula
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-004-1769-y

Plant resistance to herbivores can be influenced not only by the independent effects of plant genotype and environmental variation, but by interactions between the two. The main aim of this study was to assess the effects of environmental variability (nutrient treatment) on the known genetic-based expression of resistance and defensive chemistry of Eucalyptus globulus to browsing by the generalist mammalian herbivore Trichosurus vulpeculaf. In a captive feeding trial, we measured intake of seedling from one relatively resistant (Blue Gum Hill) and one relatively susceptible (St Helens) population of E. globulus grown under two nutrient treatments (no fertiliser, plus fertiliser). There was a significant genotype×fertiliser interaction effect on intake of E. globulus foliage by T. vulpecula, and the predicted genetic-based resistance of the two populations was expressed only for the non-fertilised treatment. Expression of resistance largely reflected the combined and inverse effects of nitrogen and condensed tannin concentrations. The expression of plant secondary metabolite concentration differed between compounds, but in all cases the effects of plant genotype and fertiliser treatment were independent. The formylated phloroglucinol compounds differed significantly between genotypes but not between fertiliser treatments. In contrast, the effect of plant genotype on the expression of condensed tannins was weak but they were significantly reduced by fertiliser. Essential oils were influenced by both plant genotype and fertiliser treatment and were significantly higher in the fertilised seedlings than in the non-fertilised seedlings. This study highlights interactive effects of plant genotype and environment in influencing the phenotypic expression of resistance in a eucalypt species to a mammalian browser. It also demonstrates that this interactive effect is the net result of independent effects of genotype and environment on plant chemistry and finally, that different groups of compounds within a plant can respond very differently to variation in environmental conditions.