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The effects of ethylenediurea and sodium erythorbate on photosynthetic function of ozone-exposed loblolly pine seedlings
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In separate experiments, ozone-sensitive loblolly pine (Pinus taeda L.) seedlings were treated with either 0 ppm, 150 ppm or 300 ppm ethylenediurea (EDU) or 0 ppm, 1030 ppm, or 2060 ppm Ozoban every 14 days. The seedlings were grown in open-top chambers in east Texas for one growing season beginning in April 1994 while being exposed to either sub-ambient (CF), approximate ambient (NF), 1.5Y,, 2.OX, or 2.5X ambient ozone levels. Net photosynthesis (A), stomatal conductance (g), and chloroplast pigment content (chlorophyll a and b, and total carotenoids),were determined every month and total foliar nitrogen concentration was determined every other month beginning in June. Although no consistent antioxidant treatment effects were observed, linear regression analysis indicates that both antioxidants show promise in providing protection from ozone injury. EDU at 150 ppm and Ozoban at 1030 ppm may retard stomatal closure in younger pine seedlings. Seedlings treated with 1030 ppm Ozoban in June had higher A with increasing ozone compared to controls. At sub-ambient ozone levels, 1030 ppm Ozoban showed signs of reducing A in younger seedlings. Neither antioxidant consistently protected chloroplast pigment content from ozone injury, however, 2060 ppm Ozoban appeared to be harmful to chlorophyll a and carotenoids. No significant EDU effects were observed with total leaf nitrogen concentration until the final sampling period in October where foliage treated with 300 ppm EDU displayed higher nitrogen concentration at all ozone levels except 1.5X ambient ozone. Foliage treated with 150 ppm EDU showed the lowest nitrogen concentration in CF and NF, but the highest in 1.5X. Ozoban-treated foliage displayed no significant antioxidant effects with regard to leaf nitrogen concentration throughout the study. Ozone effects were observed early in the study for all variables, but over time, as ambient ozone levels declined, ozone effects became inconsistent. Because of the relatively low ambient ozone levels in east Texas for the season (compared to that of the past five years) and the abundant top growth of seedlings in CF and NF, the results of this study do not conclusively show that EDU or Ozoban provide adequate protection from ozone injury to loblolly pine seedlings in open-top chambers.
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Kuehler, Eric Anthony (1995). The effects of ethylenediurea and sodium erythorbate on photosynthetic function of ozone-exposed loblolly pine seedlings. Master's thesis, Texas A&M University. Available electronically from
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