Date of Graduation

2005

Document Type

Dissertation/Thesis

Abstract

I investigated whether seedlings of non-agricultural plants exposed to varying levels of UV-B exposure had altered growth, physiological, and tissue chemistry responses under changing environmental conditions. In a field experiment, using a modulated UV-B lamp bank system, elevated UV-B did not significantly alter the total biomass of the 6 plant species that were studied, and only Quercus rubra showed a trend towards some sensitivity to UV-B. In two species—Platanus occidentalis and Setaria faberii—I found an increase in the production of UV-B absorbing compounds under elevated UV-B while two grasses—S. faberii and Elymus virginicus—had significantly decreased C:N ratios under elevated UV-B. However, only the leaf litter of S. faberii grown under elevated UV-B underwent significant mass losses. In my second study Q. rubra was exposed to varying UV-B and N availability in a greenhouse experiment. The sensitivity of Q. rubra to UV-B depended interactively on UV-B dose and nitrogen availability but not in the direction predicted. These responses were apparent in the effect of UV-B on both aboveground and belowground measurements. The observed changes in the effect of UV-B on photosynthesis were inconsistent with changes in the production of UV-B screening compounds. In my third experiment when Q. rubra was exposed to varying UV-B and water availability in a greenhouse, the UV-B effect on total biomass was significantly reduced only at the ambient UV-B level and mostly as a result of changes in the below-ground and total biomass component. The observed response to UV-B corresponded well with the UV-B effect on light saturated photosynthesis (Asat) and chlorophyll fluorescence at the ambient dose. The UV-B effect on some above-ground components (stem mass, plant height and specific leaf mass, above-ground biomass) did depend upon the water availability, such that with increasing soil moisture exposure to UV-B effect reduced these growth parameters. Finally, in my fourth study, where Q. rubra seedlings were exposed to a change in UV-B due to a canopy gap while receiving varying levels of N, UV-B had a significant interactive effect with N availability on only one measured variable—stem mass—such that seedlings under ambient UV-B exposure were most sensitive. Overall, I determined that the UV-B sensitivity of some non-agricultural species was species-specific, and depended on the levels of other environmental variables, such as N and water availability. However, no consistent pattern of UV-B response was observed for Q. rubra across the various experiments. Since Q. rubra is a long-lived, perennial tree species, it may be more prudent to conduct longer-term experiments as relatively small UV-B effects can potentially accumulate over the plant's lifespan. Further, such experiments should also manipulate or account for the varied response to UV-B under changing climate and environmental conditions.

Download

Share

COinS