PARENT SESSION
Poster Session 34: Herbivory
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
The effects of light, wind, competition, and handling on leaf chemistry and herbivory in Apocynum cannabinum.
Niesenbaum, Richard*,1, Cahill, James2, Ingersoll, Christine1, Strollo, Christine 1, 1 Muhlenberg College, Allentown, PA, USA2 University of Alberta, Edmonton, Alberta, Canada
ABSTRACT- Levels of herbivory are highly variable in space and time and are influenced by a plant's microhabitat. Microhabitat is in turn influenced by biotic factors such as shading by neighbors, trampling, and stem flexure. These latter two factors are routinely imposed by experimental activity in field studies. We examined how light competition, experimental activity, local light environment, and wind interact to influence leaf chemistry and herbivory in Apocynum cannabinum. In the field, both tying back plant neighbors, and repeated experimental activity increased light reaching focal plants, plant size, leaf cardenolide concentration, leaf carbon, and herbivory. Herbivory was greater on plants which had higher C:N ratios and more leaves. In the greenhouse, touching plants without manipulating their light environment resulted in increased plant height, increased %C of leaves, but did not influence cardenolide concentration. Wind alone increased leaf number, but not plant height or %C. It appears that changes to the local light environment have pronounced impacts on the growth, chemistry and herbivory of this focal species. However, whether the specific mechanism that altered light was experimental activity or intentional tieback on neighbors made no difference. This surprising result indicates that for this species, simply visiting the plant has the same biological effect as removing all aboveground competitors. Additionally the light levels altered C:N ratios, with this appearing to be a more important determinant of herbivory than cardenolide concentrations in the species. Physical manipulation by experimenter touch and wind influence plant morphology and toughness, but do not influence leaf chemistry.
Key words: herbivory, leaf chemistry, competition, Apocynum cannabinum