Correlations between leaf toughness and phenolics among species in contrasting environments of Australia and New Caledonia

†Background and Aims Plants are likely to invest in multiple defences, given the variety of sources of biotic andabiotic damage to which they are exposed. However, little is known about syndromes of defence across plantspecies and how these differ in contrasting environments. Here an investigation is made into the associationbetween carbon-based chemical and mechanical defences, predicting that species that invest heavily in mechan-ical defence of leaves will invest less in chemical defence.†Methods A combination of published and unpublished data is used to test whether species with tougher leaveshave lower concentrations of phenolics, using 125 species from four regions of Australia and the Pacific island ofNew Caledonia, in evergreen vegetation ranging from temperate shrubland and woodland to tropical shrublandand rainforest. Foliar toughness was measured as work-to-shear and specific work-to-shear (work-to-shear perunit leaf thickness). Phenolics were measured as ‘total phenolics’ and by protein precipitation (an estimate oftannin activity) per leaf dry mass.†Key Results Contrary to prediction, phenolic concentrations were not negatively correlated with either measureof leaf toughness when examined across all species, within regions or within any plant community. Instead,measures of toughness (particularly work-to-shear) and phenolics were often positively correlated in shrublandand rainforest (but not dry forest) in New Caledonia, with a similar trend suggested for shrubland in south-western Australia. The common feature of these sites was low concentrations of soil nutrients, with evidenceof P limitation.†Conclusions Positive correlations between toughness and phenolics in vegetation on infertile soils suggest thatadditive investment in carbon-based mechanical and chemical defences is advantageous and cost-effective inthese nutrient-deficient environments where carbohydrate may be in surplus.Key words: Antiherbivore defence, leaf toughness, mechanical defence, chemical defence, phenolics, trade-offs.