title: Correlations between leaf toughness and phenolics among species in contrasting environments of Australia and New Caledonia.
abstract: OBJECTIVE
  Plants are likely to invest in multiple defences, given the variety of sources of biotic and abiotic damage to which they are exposed. However, little is known about syndromes of defence across plant species and how these differ in contrasting environments. Here an investigation is made into the association between carbon-based chemical and mechanical defences, predicting that species that invest heavily in mechanical 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  A combination of published and unpublished data is used to test whether species with tougher leaves have lower concentrations of phenolics, using 125 species from four regions of Australia and the Pacific island of New Caledonia, in evergreen vegetation ranging from temperate shrubland and woodland to tropical shrubland and rainforest. Foliar toughness was measured as work-to-shear and specific work-to-shear (work-to-shear per unit leaf thickness). Phenolics were measured as 'total phenolics' and by protein precipitation (an estimate of tannin activity) per leaf dry mass.
  
  
  RESULTS
  Contrary to prediction, phenolic concentrations were not negatively correlated with either measure of 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 shrubland and 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 evidence of P limitation.
  
  
  CONCLUSIONS
  Positive correlations between toughness and phenolics in vegetation on infertile soils suggest that additive investment in carbon-based mechanical and chemical defences is advantageous and cost-effective in these nutrient-deficient environments where carbohydrate may be in surplus.
authors.affiliation: School of Biological Sciences, Monash University, Victoria 3800, Australia. jenny.read@sci.monash.edu.au
authors.forename: Jennifer
authors.initials: J
authors.lastname: Read
authors.forename: Gordon D
authors.initials: GD
authors.lastname: Sanson
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Caldwell
authors.forename: Fiona J
authors.initials: FJ
authors.lastname: Clissold
authors.forename: Alex
authors.initials: A
authors.lastname: Chatain
authors.forename: Paula
authors.initials: P
authors.lastname: Peeters
authors.forename: Byron B
authors.initials: BB
authors.lastname: Lamont
authors.forename: Michel
authors.initials: M
authors.lastname: De Garine-Wichatitsky
authors.forename: Tanguy
authors.initials: T
authors.lastname: Jaffré
authors.forename: Stuart
authors.initials: S
authors.lastname: Kerr
mesh_terms: D001315:Australia; D001696:Biomechanical Phenomena; D004777:Environment; D009510:New Caledonia; D010636:Phenols / Q000032:analysis*; D018515:Plant Leaves / Q000502:physiology*; D013045:Species Specificity; D013634:Tannins / Q000378:metabolism; D014197:Trees / Q000502:physiology*
chemical_list: D010636:Phenols; D013634:Tannins