Disertation Research: Nitrogen-Plant-Insect Interactions: Integrating Via a Net Effects Approach

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9423316 Coleman Nitrogen fertilization is well known to both increase plant productivity and insect herbivore damage. Certain levels and rates of fertilization may negatively affect plant productivity by increasing the amount of damage by insects. This research will examine the net impact of two insect herbivores on two plant species grown under various fertilization regimes. It is designed specifically to understand the consequences of fertilization and insect herbivory in combination on plant productivity. Two economically and ecologically important tree species (oak and cottonwood) with contrasting life history traits and two economically detrimental insect herbivore species are the subjects. Fertilization experiments will be carried out in both a planted field plot and, for control and comparison purposes, in a greenhouse. Samples of each tree species will be exposed to differing fertilization schedules in the presence and absence of insect herbivores, and effects on plant growth, tissue chemistry, and herbivore performance will be measured. The results of this study should improve understanding of the impact on plant productivity of fertilization levels and rates of addition, in the presence and absence of insect herbivores. They will reveal when tradeoffs occur between positive effects of fertilization on plant growth and negative effects of fertilization through stimulation of insect feeding on plants. The long term result may include the formulation of fertilization practices that optimize net productivity of plants, yet reduce fertilizer and pesticide requirements.