The ability to simulate enriched CO2 atmospheres provides a unique opportunity to: 1) study the dynamics of plant/herbivore interactions under these conditions; and 2) examine plant allocation patterns under controlled carbon and nitrogen availabilities. The nutritional ecology and fitness of herbivores feeding on plants grown in enhanced CO2 environments over several generations will be investigated. In addition, the effects of herbivores on plant fitness under different CO2 conditions will be compared. Plantago lanceolata (Plantaginaceae), a herbaceous perennial which contains iridoid glycosides, and a specialist herbivore, Junonia coenia (Lepidoptera: Nymphalidae), which uses these compounds as feeding and oviposition stimulants, will serve as an excellent system to study these interactions. To examine trade-offs in allocation of carbon and nitrogen resources to growth, reproduction, and defense, individuals of two plant species, differing in the classes of allelochemicals they contain, will be grown under varying carbon (CO2) and nitrogen availabilities. Growth, reproductive output and allelochemical content will be determined for P. lanceolata (which contains iridoid glycosides) and Penstemon digitalis (Scrophulariaceae) which contains both nitrogen-based (alkaloids) and carbon-based (phenolics and iridoid glycosides) allelochemicals.
