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-li ved 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 nutrien t-poor woodland in eastern Australia. Fracture properties of leaves (force of fracture, tissue toughness) and other leaf traits [LMA, thickness, dry-m atter content (DMC), leaf area] were measured for each species and evaluate d 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 expla ined approximately 30-40% of variation in leaf lifespan. Leaf toughness exp lained 25% of variation in leaf lifespan, and DMC 12%. Leaf toughness and D MC were correlated with each other, but not with leaf thickness. Leaf thick ness 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 Nutrients can be withdrawn prior to leaf death and redeployed elsewhere in the canopy when leaf death is initiated by a plant.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 contro l is external to the plant these nutrients are lost. There may be advantage s to increasing defence to give a high likelihood that the plant has contro l over the timing of leaf death.