Intra-plant variation in cyanogenesis and the continuum of foliar plant defense traits in the rainforest tree Ryparosa kurrangii (Achariaceae)
Bruce L. Webber (1, 2, 3) and Ian E. Woodrow (1)
1. School of Botany, The University of Melbourne, Victoria 3010, Australia / 2. Present address: Centre d’Ecologie Fonctionnelle et Evolutive, CNRS (UMR 5175), 1919 Route de Mende, 34293 Montpellier Cedex
05, France / 3. Corresponding author () / Received August 19, 2007; accepted February 5, 2008; published online April 1, 2008
Summary
At the intra-plant level, temporal and spatial variations in plant defense traits can be influenced by resource requirements,
defensive priorities and storage opportunities. Across a leaf age gradient, cyanogenic glycoside concentrations in the rainforest
understory tree Ryparosa kurrangii B.L. Webber were higher in young expanding leaves than in mature leaves (2.58 and 1.38 mg g–1, respectively). Moreover, cyanogens, as an effective chemical defense against generalist herbivores, contributed to a defense
continuum protecting foliar tissue during leaf development. Chemical (cyanogens and phenolic compounds) and phenological (delayed
greening) defense traits protected young leaves, whereas mature leaves were largely protected by physical defense mechanisms
(lamina toughness; explained primarily by leaf mass per area). Cyanogen concentration was considerably higher in floral tissue
than in foliar tissue and decreased in floral tissue during development. Across contrasting tropical seasons, foliar cyanogenic
concentration varied significantly, being highest in the late wet season and lowest during the pre-wet season, the latter
coinciding with fruiting and leaf flushing. Cyanogens in R. kurrangii appear to be differentially allocated in a way that maximizes plant fitness but may also act as a store of reduced nitrogen
that is remobilized during flowering and leaf flushing.
