Time-resolved fluorescence of conifers exposed to environmental pollutants.

With regard to an early diagnosis of defects within the photosynthetic system of conifers by air pollutants, we measured the chlorophyll fluorescence from microscopic parts of individual pine and spruce needles. In particular, different spruces had been exposed before to well-defined doses and concentrations of ozone and SO2. In addition to spectral distributions and time courses of fluorescence intensity, fluorescence lifetimes were detected after picosecond laser pulse excitation. Time constants of tau 1 = (0.10 +/- 0.02) ns and tau 2 = (0.50 +/- 0.10) ns were measured for intact photosynthesis; an increase of tau 2 and a further time constant tau 3 = (2.5 +/- 0.5) ns were found, if defects within the photosynthetic system occurred. Most significant defects were so far measured after exposition to high ozone doses during longer time periods.