Efeito da luminosidade nas características de defesa contra herbívoros de Inga paraensis Ducke (Fabaceae: Mimosoideae)

Abstract

The formation of treefall gaps in tropical forests has a profound effect on plants growing in the understory, specifically due to increased light availability. We examined plasticity to light of antiherbivore traits, focusing on expanding leaves, the phase where the majority of herbivory occurs. We sampled Inga paraensis (Fabaceae) saplings along a light gradient in a terra-firme forest in Central Amazonia. We quantified the following traits: leaf production and expansion time; dry mass of total phenolics, saponins and nitrogen; ants attracted to extrafloral nectaries; and leaf consumption. Regression models were performed with a combination of young leaf traits by principal component analysis (PCA) as predictor to leaf consumption. We found saplings growing under a wide range of light conditions, from deeply shaded understory (0.4% canopy openness) to large gaps (13.3%). Light intensity positively affected the number of leaves produced per flush and the mass of phenolic compounds, but had no effect on any other trait. On average, 39% of leaf area was consumed with no difference across the light gradient. A PCA of leaf traits revealed four principal components that explained 87% of the variation among plants. In general, traits were combined into leaf chemical composition and traits affecting leaf growth. Linear regression of herbivory as a function of growth traits showed the leaf consumption was best explained by slow-expansion of leaves and fewer leaves produced per flush. Thus, unlike studies of mature leaves, young leaves of I. paraensis show remarkably little plasticity in defense traits across a light gradient, suggesting that young leaf development is due to a canalized physiological process.