. 9509089 Karowe When plants are grown under elevated carbon dioxide, their leaves usually contain less nitrogen but may contain more, less, or the same amount of defensive chemicals. This research asks two main questions: !) Do CO2-induced changes in plant quality affect higher trophic levels (e. g. caterpillars that consume plants, parasitoid wasps that develop inside and consume caterpillars, and hyperparasitoid wasps that develop inside and consume parasitoid wasps), and 2) Does association of host plants with nitrogen-fixing bacteria buffer all trophic levels against the direct effects of elevated CO2? To answer these questions, the effects of elevated CO2 on plant nutritional quality and defensive chemistry, and subsequent effects on herbivores, parasitoids, and hyperparasitoids will be compared between a four trophic level system based on crucifer (non-nitrogen fixing) host plants and one based on legume (nitrogen fixing) host plants. This research will expand our understanding of the ecological consequences of elevated CO2 to include the third and fourth trophic levels, and to begin to assess the mechanisms responsible for variability among different multiple trophic level systems in their susceptibility to the direct effects of elevated CO2. Because our economically important agricultural crops include both legumes and non-legumes, and support multiple trophic levels, this information may enhance agricultural productivity under the future, i. e., elevated CO2 atmosphere.
