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- Title
Physiological effects of a long term exposure to low concentrations of NH<sub>3</sub>, NO<sub>2</sub> and SO<sub>2</sub> on Douglas fir (Pseudotsuga menziesii).
- Authors
van Hove, L. W. A.; Bossen, M. E.; Mensink, M. G. J.; van Kooten, O.
- Abstract
The above-ground parts of two years old seedlings of Douglas fir (Pseudotsuga menziesii) were exposed to filtered air, NH3, NO2, SO2 (66, 96 and 95 μg m-3, respectively), to a mixture of NO2 + NH3 (55 + 82 μg m-3) or SO2 + NO2 (128 + 129 μg m-3), for 8 months in fumigation chambers. Both chlorophyll fluorescence and gas exchange measurements were carried out on shoots which had sprouted at the beginning of the exposure period. The chlorophyll fluorescence measurements were performed after 3 and 5 months of exposure (average shoot age 70 and 140 days, respectively). Light response curves of electron transport rate (J) were determined, in which J was deduced from chlorophyll fluorescence. In addition, light response curves of net CO2 assimilation were determined after 5 months of exposure. After 3 months of exposure (average shoot age 70 days) all exposure treatments showed a lower maximum electron transport rate (Jmax) as compared to the control shoots (filtered air). A large reduction (45%) was observed for shoots exposed to SO2 + NO2. During the exposure period between 3 and 5 months (average shoot age 70 and 140 days, respectively) a decrease of Jmax was observed for all treatments. Jmax had further declined some time after termination of the exposure, when average shoot age was 310 days. Shoots exposed to SO2 and SO2 + NO2 also showed a reduction in maximum net CO2 assimilation (Pmax) as compared to the control shoots. However, shoots exposed to NO2 showed no reduction and even a higher Pmax was observed for shoots exposed to NH3 or NO2 + NH3. Needles of these treatments also showed a higher chlorophyII content which might explain the contradictory result obtained for these treatments; the increased amount of photosynthetic units counteracts the reduction in Jmas and consequently no reduction in Pmax is measured. Shoots exposed to SO2 and SO2+NO2 also showed a reduction in maximum stomatal conductance. However, the stomatal opening was larger than could be expected on basis of their (maximum) Co2 assimilation rate. Consequently, water use efficiency of these shoots was lower than that of the control shoots. Also shoots exposed to NO2 had a lower water use efficiency due to a significantly higher maximum g., Shoots exposed to NH3 showed a high transpiration rate in the dark, indicating imperfect stomatal closure.
- Subjects
PHOTOSYNTHETIC pigments; PORPHYRINS; CHLOROPLAST pigments; PSEUDOTSUGA; PHOTOSYNTHETIC reaction centers; WATER efficiency
- Publication
Physiologia Plantarum, 1992, Vol 86, Issue 4, p559
- ISSN
0031-9317
- Publication type
Article
- DOI
10.1111/j.1399-3054.1992.tb02170.x