Detection of Changes in Steady-State Chlorophyll Fluorescence in Pinus strobus Following Short-term Ozone Exposure

Abstract

Summary Steady-state chlorophyll fluorescence measured with a laboratory fluorescence spectrophotometer has been used successfully, in repetitive experiments, to detect changes in the red/far-red (R/FR) emission intensity ratio of white pine (Pinus strobus L.) induced by fumigation with ozone. Experiments were conducted in 1992 and 1993 as part 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 made 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 180 mm' m-'). The R/FR fluorescence ratio mean from the spectra collected 24 hours after exposure was significantly different from the pre-fumigation R/FR ratio mean (P = .10). In August, 1992, the R/FR ratio mean at 24 hrs post-fumigation was significant at P = .05. In August, 1993 measurements were made, prior to, one hour after, 24 hours after, and 48 hours after exposure, with a different set of white pine ramets exposed to 120 and 220 mm' m-' ozone for 3 hours. The R/FR ratio means at 24 hrs post-fumigation were significant at P = .05 for the 120 mm' m-' ozone exposure and at P = .20 for the 220 mm' m-' ozone exposure. Differences between the R/FR ratio means of pre- and 24 hrs post-fumigation measurements for 120, 180, and 220 mm' m-' ozone indicate dose dependent responses. The 220 mm 3m-' ozone exposed 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, derived from chlorophyll emissions at wavelengths corresponding to known atmospheric and solar absorption features, indicates that stress-induced fluorescence changes may be detectable in direct sunlight.