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Ozone needles loblolly pines ... and saps sequoia seedlings.

Ozone needles loblolly pines . . .

Wood merchants love the long-neded loblolly for its ability to reach timber size in 25 to 30 years. This pine represents the major commercial wood species of the South, a region producing half of the United States' wood fiber. But in the past two decades, loblolly growth rates in the South have decreased by 10 to 15 percent. Most experts have blamed air pollution, fingering rising levels of ozone -- a pollutant already held responsible for about 90 percent of U.S. crop losses from air pollution (SN: 6/6/87, p.357).

Supporting that theory, Duke University researchers have found that high levels of ozone diminish long-term photo-synthesis rates in the loblolly pine. Duke ecologist Curtis J. Richardson calls the research the "first large-scale field study to look at levels of ozone in the Southweast that are significantly affecting photosyntheis and tree growth" of loblolly pines.

Richardson and his colleagues studied trees in a 50-acre experimental forest site near the university in Durham, N.C. They exposed trees in 54 chambers to five different levels of ozone and three of acid rain. At ozone levels triple those normally found in forest air, loblollies experienced an 80 percent reduction in photosynthesis compared with trees exposed to ambient ozone levels, the researchers reported in Toronto last month at the meeting of the American Institute of Biological Sciences. Similar ozone levels now exist in such large cities as Atlanta and Houston. At slightly lower ozone levels, loblolly needles -- which normally stay on the tree for 14 to 18 months -- dropped off in the first year, Richardson says. New needles showed an unexplained increase in their photo-synthetic rate, which leveled off as cumulative ozone exposure increased. Duke scientists next hope to determine whether the trees will produce enough new needles to offset the early loss of old ones.

In another study, described in the June PLANt PHYSIOLOGY, Richardson and Duke toxicologist Richard T. Di Giulio determined that loblolly pines, red spruce and scotch pines exposed to similarly high ozone levels produced increased levels of enzymes and other compounds called antioxidants. Plants produce antioxidants to prevent the formation of hydroxyl radicals, highly reactive molecules that usually kill cells. Richardson says the increased antioxidant levels reflect the trees' attempt to overcome oxygen stress. Scientists could look for increased antioxidant levels in needles as a biomarker of air pollution stress, he told SCIENCE NEWS.
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Publication:Science News
Date:Sep 16, 1989
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