Effects of light regime on antioxidant content of foliage in a tropical forest community

A basic tenet of plant ecology is that under high light and limiting nutrient levels, carbon becomes relatively more available for investment in anti-herbivore defense. Rarely considered in discussions of such defense investments, however, is the necessity for plants to defend themselves against oxidative damage caused by light exposure itself. To determine if the ability to respond to elevated levels of light exposure by increasing production of antioxidant compounds is a general characteristic of foliage in tropical plants, we conducted a broad survey of antioxidant content in foliage of 55 species in a tropical forest community by comparing individuals within forest gaps to conspecifics in the closed canopy forest. To do so, we devised a rapid assay to use under field conditions. Of the 41 species of shrubs, trees, and lianas demonstrating a discernible difference in antioxidant content under the two light regimes, 34 (68%) showed higher antioxidant content under high light conditions. In a quantitative laboratory-based study using four of these species, light was associated with a 15 to 45 percent increase in water-soluble antioxidants in three species; one species displayed a 118 percent increase in fat-soluble antioxidants as well. Thus, changes in the chemistry of plant foliage in response to light may reflect plant investments in defense against abiotic stress factors as well as investments in defense against biotic stress factors.