Influence of plant ontogeny on compensation to leaf damage

Ontogenetic changes in architecture, carbohydrate reserves, and resource allocation can constrain the ability of plants to compensate for herbivore damage. To evaluate ontogenetic changes in compensation, saplings and reproductive individuals of the tropical tree Casearia nitida were subjected to three levels of defoliation (0, 25, and 75% leaf area removed) and regrowth was quantified. The impact of defoliation on fruit production was evaluated in reproductive trees. In addition, the influence of defoliation on carbohydrate reserves and on the production of phenolic compounds was assessed. Plants at both stages were able to compensate for 25% leaf area loss, but only saplings were able to compensate at the 75% defoliation level. Negative impacts of defoliation on reproductive trees were also suggested by their tendency to produce fewer fruits when defoliated. The concentration of nonstructural carbohydrates decreased with damage in saplings but not in reproductive trees, suggesting an ontogenetic stage-dependent impact of defoliation on carbohydrate reserves. The concentration of phenolic compounds in leaves decreased with increasing leaf damage in both ontogenetic stages. This suggests a resource based trade-off between defense and compensation. The results from this study suggest that ontogeny needs to be considered when assessing plant responses to herbivore damage.