Global atmospheric CO2 levels are rising, and current levels may double by the latter half of the 21st century. Elevated CO2 is known to alter plant physiology and growth, but very little research has addressed the consequences of elevated CO2 for the ecological interactions of plants. A couple of studies have documented significant effects of CO2 on interactions between herbaceous plants and insects, but nothing is known about effects of CO2 on interactions between trees and tree-feeding insects. The purpose of this research is to investigate the effects of enriched CO2 atmospheres on interactions between deciduous trees and tree-feeding insects, as mediated by changes in tree chemical composition. The model system will consist of quaking aspen, red oak and maple (fast-, intermediate- slow-growing species, respectively) and two leaf- feeding insects, the gypsy moth and forest tent caterpillar. Resource availability theory is used as a framework for development of three primary goals and associated hypotheses. The three goals of this research are to: 1) determine the effects of elevated CO2 on tree chemical composition, and consequences for performance (survival, growth, food use efficiencies) of insects, 2) investigate the interactive effects of elevated CO2 and soil nutrient availability on tree chemical composition and insect performance, and 3) determine the interactive effects of elevated CO2 and defoliation on tree chemical composition and insect performance. Trees will be grown under several concentrations of CO2 in environmental control rooms at the University of Wisconsin Biotron, and subjected to chemical assays and bioassays. Significant features of this research include its focus on CO2-mediated effects on interactions between forest trees and their defoliators, an emphasis on effects of CO2 on plant chemical composition, an emphasis on interactive effects between CO2 and their environmental "stresses" on plant-insect interactions, and use of three tree species and two insect species that are ecologically and economically important components of North American deciduous forest.
