Steady-state chlorophyll fluorescence red/far-red emission ratio increases detected from Pinus strobus after short-term ozone exposure

Steady-state chlorophyll fluorescence measurements of white pine (Pinus strobus L.) exposed to predetermined levels of ozone, have shown significant increases in red/far-red (R/FR) emission intensity ratios in experiments that were part of a study of the effects of short-term ozone exposure to native plants at Acadia National Park, Maine. Laboratory spectrophotometer measurements were made of clonal grafts (ramets) of white pine, prior to, one hour after, and 24 hrs after exposure to ozone (3 hrs duration at 180 mm³m^-3). The R/FR fluorescence ratio mean derived from spectra collected 24 hrs after exposure in August 1992, was significantly different from the pre-fumigation R/FR ratio mean (P=0.05). August, 1993 measurements, with a different set of white pine ramets exposed to 120 and 220 mm³ m^-3 ozone for 3 hrs, produced R/FR ratio means at 24 hrs post-fumigation that were significant at P=0.05 and 0.20, respectively. Differences in the R/FR ratio means of pre- and 24 hrs post-fumigation measurements for 120, 180, and 220 mm³m^-3 ozone indicate dose dependent responses