Title

The role of nitrogen and leaf development in plant-insect interactions

Date of Award

1997

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

James S. Coleman

Keywords

herbivory

Subject Categories

Biology | Botany

Abstract

Increased nitrogen (N) availability to plants via fertilization, atmospheric deposition, or land use practices generally increases plant growth and tissue N concentration, and decreases tissue secondary chemical concentrations. Consequently, "N fertilized" plants should provide a greater quantity of higher quality leaf resources to insect herbivores. In turn, fertilized plants should experience greater levels of herbivory and proportionally more damage than unfertilized plants. Yet, we have had limited success in predicting both the effects of fertilization on plant tissue quality and quantity for herbivores, and the impact of herbivory on plant growth. The primary objective of this research was to increase our understanding of the effects of N fertilization on plant-insect interactions by determining the plant processes that are affected by N, and in turn, regulate herbivore responses.

The research addressed the following questions: (1) does fertilization affect the biochemical quality of leaves for herbivores through changes in leaf development? (2) does fertilization increase the availability of leaf resources for herbivores through changes in leaf development? and (3) how does fertilization influence the impact of herbivore damage on plant growth? My experimental system included: saplings of an economically and ecologically important tree species, Populus deltoides Bart.; varying N supply rates (concentration x time); two folivorous beetles, Chrysomela scripta F. and Plagiodera versicolora Laich. (Coleoptera: Chrysomelidae); and artificial defoliation.

The results demonstrated that: (1) foliage biochemical quality is mostly controlled by an interaction between fertilization and leaf development; (2) fertilization increases the availability of leaf resources that are suitable for feeding by insects to a greater extent than plant productivity; and (3) fertilization influences the effect of defoliation on plant growth by affecting the trajectory of growth through time. These results were independent of the degree to which fertilization affected plant growth rate and leaf N concentration. This research illustrates how N fertilization, through changes in leaf development and plant growth, regulates plant-insect interactions, and thus provides mechanistic predictions of the impact of fertilization on plants and herbivores.

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