The Effect of Prolonged Exposure to Air-Borne Pollutants on the Photosynthesis of Douglas Fir (Pseudotsuga menziesii) Studied with in vivo Chlorophyll Fluorescence
Two year old douglas firs were exposed to moderate concentrations of SO2, NO2, NH3 or combinations of these gases. The effect on photosynthesis of young needles (age between 20 and 135 days, which had sprouted during the fumigation treatment) was determined with Pulse Amplitude Modulated chlorophyll fluorescence (1). The electron transport rate was inferred from the fluorescence measurements by a method described by Genty et al. (2), which was found to be more appropriate for 4cpglas fir than the method described by Weis and Berry (3). The light response curves were fitted to a formula described by Leverenz (4) from which the maximal electron transport rate, the quantum yield and a measure of the convexity of the light response curve can be deduced. All treatments resulted in a reduced rate of electron transport at saturating illumination as compared to the control (exposed to filtered air). But the most severe reduction (>50%) was observed in the plants exposed to a combination of SO2 and NO2. Firs exposed to NO2 alone revealed an enhanced chlorophyll content, which was concluded from a significant decrease in the convexity of the light response curve. The plants exposed to SO2 revealed a slightly enhanced quantum yield, similarly as has been observed before in poplar shoots (5). The reduced maximal electron transport rate in fir needles fumigated with NH3 was in marked contrast to previous measurements in poplar shoots and broad beans (6–8).
KeywordsChlorophyll Fluorescence Electron Transport Rate Light Response Curve Teflon Film Maximal Electron Transport Rate
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