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KMID : 0380120010240020093
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Korean Journal of Ecology
2001 Volume.24 No. 2 p.93 ~ p.100
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Eco-physiological Responses of Two Populus deltoides Clones to Ozone
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Yun, Sung Chul
Kim, Pan Gi/Hur, Jae Seoun/Lee, Jae Cheon/Park, Eun Woo
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Abstract
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One-year-old cottonwood (Populus deltoides Bartr.) clones, which were classified as sensitive or tolerant, were exposed to 150 nl/l ozone (O_3) over 8 days for 8 hours each day under glass chamber conditions with natural sunlight. The leaves of the sensitive clone had black stipple and bifacial necrosis after O_3 treatment. Photosynthesis and stomatal conductance were measured before, during, and after the O_3 treatment. The photosynthetic rates due to O_3 treatment were decreased 51 percent and 34 percent on the sensitive and tolerant clone, respectively. The stomatal conductance of the sensitive clone was more than 40 percent higher than that of the tolerant clone regardless of the O_3 treatment. As light intensity increased, the O_3 effect on photosynthesis was clear. Compared to the previous growth chamber studies, our natural light exposure system was able to maintain a stable photosynthetic responses of the control treatment throughout the fumigation period. In additon, changes in assimilation versus intercellular CO_2 concentration (A/C, curves) showed that O_3 decreased the slope and asymptote of the curves for the sensitive clone. This indicates that O_3 decreases the biochemical capacity of photosynthesis on the sensitive clone. Chlorophyll contents and fluorescence of the two clones were analyzed to examine the O_3 effects on photosystem II, but O_3 did not impact these variables on either clone. Although the tolerant clone did not show any foliar injury, we could not find any ecophysiological defensive responses to O_3 treated. Stomatal conductance of the tolerant clone was originally much lower than that of the sensitive one. Thus, the mechanisms of the tolerant clone in this system are to narrowly open stomata and efficiently maintain photosynthesis with a more durable biochemical apparatus of photosynthesis under O_3 stress. The sensitive clone has higher photosynthetic capacity and more efficient light reaction activity than the tolerant one under charcoal filtered condition, but is not as resilient under stress.
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