AOBPreview published online on December 19, 2008
Annals of Botany, doi:10.1093/aob/mcn246
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Correlations between leaf toughness and phenolics among species in contrasting environments of Australia and New Caledonia
1 School of Biological Sciences, Monash University, Victoria 3800, Australia
2 Centre for Ecosystem Diversity and Dynamics, Department of Environmental Biology, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia
3 IAC/CIRAD UPR AGIRs, BP 73, 98890 Païta, New Caledonia
4 Laboratoire de Botanique et d'Écologie Végétale Appliquée, IRD–Institut de recherche pour le développement, Centre de Nouméa, BP A5 Nouméa 98848, New Caledonia
* For correspondence. E-mail jenny.read{at}sci.monash.edu.au
Received: 28 August 2008 Returned for revision: 30 September 2008 Accepted: 10 November 2008
Background and Aims: 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Methods: A combination of published and unpublished data is used to test whether species with tougher leaves have lower concentrations of phenolics, using 125 species from four regions of Australia and the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.
Key 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.
Key words: Antiherbivore defence, leaf toughness, mechanical defence, chemical defence, phenolics, trade-offs
Present address: Behaviour, Physiology and Ecology Research Group, School of Biological Sciences, The University of Sydney, NSW 2006, Australia
Present address: Threatened Species Branch, Environmental Protection Agency, PO Box 15155, City East QLD 4002, Australia
Present address: CIRAD, UPR AGIRs, 37 Arcturus Rd, Highlands, Harare, Zimbabwe