The Impact of Increased Atmospheric Carbon Dioxide on the Nitrogen Status and Alkaloid Content in Lupinus: Implications for Plant/Herbivore Interactions

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Increased co2 will have major impacts on plants--- including increased photosynthesis, increased growth, decreased water use, and decreased tissue nitrogen. These changes will be even more intense in legumes which have symbiotic nitrogen-fixing bacteria. Rates of nitrogen fixation are often determined by available photosynthate or size of nodules. The impact of increased co2 on two species of lupines (Lupinus) will be investigated at the Duke Phytotron. These plants have nitrogen- fixing nodules and thus are likely to have increased rates of fixation as co2 concentrations increase. In addition, lupines have alkaloids as their anti-herbivore defense compounds. Since alkaloids contain nitrogen, increased co2 is very likely to impact on alkaloid concentration as well. To study this interaction, lupines will be grown under three different concentrations of co2 and three different levels of foliage damage. Foliage from these plants will be analyzed for changes in chemical composition, and will be fed to a native species of herbivore, Orgyia vetusta. This research is the first to investigate a three-level interaction between a plant, its nitrogen-fixing symbiont, and herbivore. Results will be of great interest to those studying atmosheric gases and global change issues.