Document: ANN-3-42-19

Does light constrain seedling defense responses to herbivory?

WALTON, A.B.* ¹, T.M.SCHAEFFER ¹, F.FONTENEAU ² and J.C.SCHULTZ ¹

The Pennsylvania State University, University Park, PA, 16802, USA ¹
Institut National Agronomique Paris-Grignon, Paris, France ²

Abstract:
While plants commonly respond to high light intensities with enhanced levels of chemical defenses, we do not know if low light in the shaded understory constrains the intensity of chemical defense responses to herbivory. We conducted a field experiment in a mixed-temperate forest in central Pennsylvania to test two hypotheses: A. Light gaps promote accumulation of chemical defenses and B. Chemical defense responses to simulated herbivory are constrained by light. We treated gap and shaded seedlings of two tree species, chestnut oak (Quercus prinus) and red maple (Acer rubrum), with jasmonic acid and mechanical damage three times during one week to simulate herbivory. After one week, we harvested leaves from each species and measured levels of shikimate-based chemical defenses. Basal levels of total phenolics, condensed tannins, and hydrolyzable tannins in both species were higher in leaves from gap seedlings exposed to high light conditions, but responses to simulated herbivory were species-specific. Chestnut oak seedlings responded to simulated herbivory with enhanced levels of condensed tannins in gaps but not shaded sites, while red maple responded with higher levels of hydrolyzable tannins in the shaded sites but not in gaps. Seedling responses could have been conditioned by differences in light quality as well as light quantity. We documented significantly higher ratios of red to far red light in gaps compared to shaded sites. Current literature indicates that ratios of red to far red light regulate portions of tannin biosynthetic pathways in plants. We propose a model predicting induced tannin synthesis in microenvironments differing in light quality and quantity.

Keywords: jasmonic acid, herbivory, inducible defenses, light quality

This abstract is being presented at: 3:30 PM in session:
Oral Session #48: Anti-Predator Responses: Fish to Sagebrush.