Relationships between leaf lifespan and structural defences in a low-nutrient, sclerophyll flora

1. The spectrum between species with low leaf mass per area (LMA), short-lived leaves and high photosynthetic rate to those with high LMA, long-lived leaves and low photosynthetic rate is one of the major spectra of variation between plant species, and is of particular relevance to the 'carbon-gain strategy' of plants. 2. In this study the relationship between physical properties of leaves and their lifespan was quantified for 17 sclerophyllous species from a nutrient-poor woodland in eastern Australia. Fracture properties of leaves (force of fracture, tissue toughness) and other leaf traits [LMA, thickness, dry-matter content (DMC), leaf area] were measured for each species and evaluated as predictors of leaf lifespan in cross-species and phylogenetic analyses, and for intercorrelation with one another. 3. The LMA, mean force of fracture, leaf thickness and leaf area each explained approximately 30-40% of variation in leaf lifespan. Leaf toughness explained 25% of variation in leaf lifespan, and DMC 12%. Leaf toughness and DMC were correlated with each other, but not with leaf thickness. Leaf thickness and toughness were related closely to LMA, while DMC and LMA were only marginally correlated. 4. Nutrients can be withdrawn prior to leaf death and redeployed elsewhere in the canopy when leaf death is initiated by a plant. However, when control is external to the plant these nutrients are lost. There may be advantages to increasing defence to give a high likelihood that the plant has control over the timing of leaf death.