DETECTION OF CHANGES IN STEADY-STATE CHLOROPHYLL FLUORESCENCE IN PINUS-STROBUS FOLLOWING SHORT-TERM OZONE EXPOSURE

Steady-state chlorophyl. fluorescence measured with a laboratory fluor escence spectrophotometer has been used successfully, in repetitive ex periments, to detect changes in the red/far-red (R/FR) emission intens ity ratio of white pine (Pinus strobus L.) induced by fumigation with ozone. Experiments were conducted in 1992 and 1993 as pan: of a study of the effects of short-term ozone exposure to native plants at Acadia National Park, Maine. In July, 1992, fluorescence measurements were m ade of clonal grafts (ramets) of native white pine, prior to, one hour after, and 24 hours after exposure to ozone (duration of 3 hours at 1 80 mm(3) m(-3)). The R/FR fluorescence ratio mean from the spectra col lected 24 hours after exposure was significantly different from the pr e-fumigation R/FR ratio mean (P = .10). In August, 1992, the R/FR rati o mean at 24 hrs post-fumigation was significant at P = .05. In August , 1993 measurements were made, prior to, one hour after, 24 hours afte r, and 48 hours after exposure, with a different set of white pine ram ets exposed to 120 and 220 mm(3) m(-3) ozone for 3 hours. The R/FR rat io means at 24 hrs post-fumigation were significant at P = .05 for the 120 mm(3) m(-3) ozone exposure and at P = .20 for the 220 mm(3) m(-3) ozone exposure. Differences between the R/FR ratio means of pre- and 24 hrs post-fumigation measurements for 120, 180, and 220 mm(3) m(-3) ozone indicate dose dependent responses. The 220 mm(3) m(-3) ozone exp osed ramets produced an R/FR ratio mean at 48 hrs post-fumigation that was lower than the 24 hrs post-fumigation R/FR ratio mean (.50 > P > .25), suggesting a potential recovery of photosynthetic processes from the effects of ozone exposure. Red/far-red fluorescence ratios, deriv ed from chlorophyll emissions at wavelengths corresponding to known at mospheric and solar absorption features, indicates that stress-induced fluorescence changes may be detectable in direct sunlight.