Title: Plant response to global change
Description: Changes in global environmental conditions, including the concentration of atmospheric carbon dioxide, temperature, and soil nutrients, will have varying effects on the performance of plant species and insect herbivores. Atmospheric CO 2 concentrations and nitrogen availability are both critical environmental variables controlling the growth and chemistry of plant species. The plant-mediated responses of phloem feeding aphids and leaf chewing insects to changes in these environmental conditions were examined in a series of experiments. Phloem feeding aphids and leaf chewing insects were used to study the feeding preferences and long-term performance of the insect species when feeding on plants grown under different conditions. Global change conditions affected both plant and insect herbivores, however the interactions between different environmental factors that sometimes affected plant traits did not affect insect herbivores. Plant species identity had the largest effect on insect herbivore performance, while global change factors had the largest effects on herbivores feeding on less preferred plant species.

The influence of photosynthesis physiology on plant responses to global change factors was also examined using species from the dicot genus Flaveria. Flaveria is a remarkable group of species with a variety of photosynthetic types including C 3 , C 4 , and intermediate species. The current distributions and physiological traits of seven Flaveria species in south-central Mexico were recorded. Life history and disturbance regime, rather than C 4 cycle characteristics, appear to be the primary controllers of Flaveria distributions in this region. The most recently described species in the genus. Flaveria kochiana, was found to use an efficient C 4 cycle, with the highest carboxylation efficiencies reported for Flaveria species. The CO 2 and temperature responses of closely related C 3 , intermediate, and C 4 plant species in the genus Flaveria were also examined. Positive responses to elevated CO 2 but negative responses to high temperature in the C 4 and intermediate species were observed. The C 3 species also showed increased performance in response to elevated CO 2 but was not affected by high growth temperature. The results indicate that the degree of C 4 photosynthetic pathway development does not predict the response of N use efficiency, photosynthetic efficiency or photo-respiratory carbon losses. Further field study of this unique group of plants will improve our understanding of the environmental conditions that promote the evolution of C 4 photosynthetic traits in dicot species.