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Physiological effects of a long term exposure to low concentrations of NH 3 , NO 2 and SO 2 on Douglas fir ( Pseudotsuga menziesii )
Author(s) -
Hove L. W. A.,
Bossen M. E.,
Mensink M. G. J.,
Kooten O.
Publication year - 1992
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1992.tb02170.x
Subject(s) - shoot , fumigation , zoology , horticulture , chlorophyll fluorescence , chemistry , botany , chlorophyll , douglas fir , biology
The above‐ground parts of two years old seedlings of Douglas fir ( Pseudotsuga menziesii ) were exposed to filtered air, NH 3 , NO 2+ , SO 2 (66, 96 and 95 μg m −3 , respectively), to a mixture of NO 2 +NH 3 (55 + 82 μg m −3 ) or SO 2 +NO 2 (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 CO 2 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 (J max ) as compared to the control shoots (filtered air). A large reduction (45%) was observed for shoots exposed to SO 2 +NO 2 . During the exposure period between 3 and 5 months (average shoot age 70 and 140 days, respectively) a decrease of J max was observed for all treatments. J max had further declined some time after termination of the exposure, when average shoot age was 310 days. Shoots exposed to SO 2 and SO 2 +NO 2 also showed a reduction in maximum net CO 2 assimilation (P max ) as compared to the control shoots. However, shoots exposed to NO 2 showed no reduction and even a higher P max was observed for shoots exposed to NH 3 or NO 2 +NH 3 . Needles of these treatments also showed a higher chlorophyll content which might explain the contradictory results obtained for these treatments: the increased amount of photosynthetic units counteracts the reduction in J max and consequently no reduction in P max is measured. Shoots exposed to SO 2 and SO 2 +NO 2 also showed a reduction in maximum stomatal conductance (g s ). However, the stomatal opening was larger than could be expected on basis of their (maximum) CO 2 assimilation rate. Consequently, water use efficiency of these shoots was lower than that of the control shoots. Also shoots exposed to NO 2 had a lower water use efficiency due to a significantly higher maximum g s . Shoots exposed to NH 3 showed a high transpiration rate in the dark, indicating imperfect stomatal closure.