CONSEQUENCES OF ENRICHED ATMOSPHERIC CO2 AND DEFOLIATION FOR FOLIAR CHEMISTRY AND GYPSY-MOTH PERFORMANCE

Elevated concentrations of atmospheric CO2 are likely to interact with other factors affecting plant physiology to alter plant chemical prof iles and plant-herbivore interactions. We evaluated the independent an d interactive effects of enriched CO2 and artificial defoliation on fo liar chemistry of quaking aspen (Populus tremuloides) and sugar maple (Acer saccharum), and the consequences of such changes for short-term performance of the gypsy moth (Lymantria dispar). We grew aspen and ma ple seedlings in ambient (similar to 360 ppm) and enriched (650 ppm) C O2 environments at the University of Wisconsin Biotron. Seven weeks af ter budbreak, trees in half of the rooms were subjected to 50% defolia tion. Afterwards, foliage was collected for chemical analyses, and fee ding trials were conducted with fourth-stadium gypsy moths. Enriched C O2 altered foliar levels of water, nitrogen, carbohydrates, and phenol ics, and responses generally differed between the two tree species. De foliation induced chemical changes only in aspen. We found no signific ant interactions between CO2 and defoliation for levels of carbon-base d defenses (phenolic glycosides and tannins). CO2 treatment altered th e performance of larvae fed aspen, but not maple, whereas defoliation had little effect on performance of insects. In general, results from this experimental system do not support the hypothesis that induction of carbon-based chemical defenses, and attendant effects on insects, w ill be stronger in a CO2-enriched world.