Effects of Photochemical Oxidant on the Growth of Poplar Cuttings

III. Effects of Ozone on Photosynthesis, Photorespiration and Dark Respiration

Abstract

The effects of ozone on apparent photosynthesis, photorespiration and dark respiration were determined in poplar (Populus × euramericana cv.'I 45/51') leaves. These results were as follows:
(1) The lower order leaves (at the 35th day after unfolding) fumigated with ozone at 0.10, 0.15, 0.20 or 0.25 ppm had apparent photosynthetic rates reduced by 3, 7, 28 and 34%, respectively, after 5 hours exposure. Apparent photosynthetic rates were recovered within a few days after fumigation.On the other hand, photosynthesis of the upper order leaves (at the 20th day after unfolding) were not affected with 0.10 or 0.20 ppm ozone for 5 hours exposure.
(2) After fumigating to poplar cuttings with 0.10 ppm ozone for 5 hours a day, 5 days a week, during the Land 2-week treatment period, apparent photosynthetic rates of the lower order leaves were reduced by 33% and 59% respectively, and photorespiratory rates were reduced by 19% and 40% respectively. But, dark respiratory rates were stimulated by 15% during the 1-week treatment. On the other hand, those of the upper order leaves were not affected by ozone fumigation.
(3) Apparent photosynthetic rates of injured leaves shown as “damage degree 3 or 5” by fumigations with 0.10 ppm ozone, 5 hours a day for 5 days, were depressed 10% and 22%, respectively, by fumigating again to 0.10 ppm ozone for 3 hours.
(4) When poplar cuttings grown in non-filtered air greenhouse and filtered air greenhouse were fumigated with 0.15 ppm ozone for 3 hours, apparent photosynthetic rates of the lower leaves in non-filtered air greenhouse were reduced by 11%, but those in filtered air greenhouse were not affected. At one day after fumigation, the rates in non-filtered air greenhouse were reduced by 28%.