LIGHT ENVIRONMENT HAS LITTLE EFFECT ON HETEROBLASTIC DEVELOPMENT OF THE TEMPERATE RAIN FOREST TREE GEVUINA AVELLANA MOL. (PROTEACEAE)

Premise of research.Heteroblastic species are those that show an abrupt change in shape and/or size among individual metamers during ontogeny. Gevuina avellana Mol. (Proteaceae) is a typical tree species in the temperate rain forests of Chile and Argentina. This tree shows drastic heteroblasty, changing from simple leaves at the seedling stage to pinnate leaves during development. It regenerates mostly in shady understories, but juveniles can be found growing under a wide range of light conditions (5%-50% canopy openness). Thus, considering that light has been proposed as a driver of the heteroblastic strategy, G. avellana is an interesting model to study the potential environmental modulation of its ontogenetically programmed heteroblasty. Therefore, the aim of this study was to determine the effect of light availability on G. avellana's heteroblastic trajectory. We postulated that G. avellana's ontogenetic changes in leaf complexity (i.e., heteroblasty) increase under high light availability.Methodology.Saplings along most of the light availability gradient were sampled. Plant height was used as a proxy for ontogeny. We measured several leaf traits (leaf area), shape (aspect ratio), pinnation (leaf dissection index), and complexity (fractal dimension index). First, we evaluated the change in each leaf trait with height by means of Pearson's correlation. Then we tested for differences in leaf traits along the ontogeny between two light environments (higher and lower than 10% canopy openness) by the line-fitting standardized major axis method.Pivotal results.We found positive correlations between each leaf trait and plant height (P < 0.001), while only leaf size and complexity showed higher ontogenetic increases under high light.Conclusions.Light environment has a small but significant effect on the heteroblastic trajectory of G. avellana. In particular, saplings inhabiting microsites with high light availability have larger and more complex leaves. While allometry would explain the ontogenetic trajectory of leaf size, the increased complexity could reflect functional advantages for large leaves in tall plants, especially under high light conditions.