Chlorophyll Fluorescence as a Measure of Ozone Induced Stress

Chlorophyll fluorescence is a nondestructive, intrinsic probe of photosynthesis. It has been used in a variety of physiological and environmental research. This study attempted to investigate the usefulness of chlorophyll fluorescence as a monitor of ozone induced stress in Quercus rubra L.

Chlorophyll fluorescence measurements were taken from mature trees and seedlings in open top chambers located at the Tennessee Valley Authority Air Pollution Research Facility at Norris, Tennessee. Chambers reflected one of three ozone concentration treatments: sub-ambient, ambient, or twice ambient. Spring leaf expansion was also measured as was spring and autumn chlorophyll content of leaves from mature trees.

Fluorescence measurements proved to reflect differences between treatments and tree size. The data indicates two response types. The first type produces an inducible response at ambient concentrations and homeostasis at twice ambient concentrations. The second type of response is homeostatic at ambient concentrations with apparent injury occurring in twice ambient treatments. These patterns indicate a multiphasic, multisite ozone effect. The fluorescence measurements indicated that seedlings were less sensitive to ozone than mature trees. No fluorescence parameters were sensitive to leaf expansion although some exhibited good correlation with seasonal changes in chlorophyll content. Treatment did not significantly affect chlorophyll content.