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Responses of Radish to All Combinations of Three Concentrations of Nitrogen Dioxide, Sulfur Dioxide, and Ozone¹

ABSTRACT

Vegetation stress by air pollutants is frequently a result of a multiple pollutant exposure. Long-range transport of major air pollutants may affect rural agricultural and forested regions of the eastern United States. Also, changes in the relative importance of the major phytotoxic pollutants, NO₂, SO₂, and O₃, can be anticipated as a result of changing energy patterns. In experiments designed to evaluate the effects of the coincident occurrence of NO₂, SO₂, and O₃, as well as the importance of the ratios of the pollutants to one another, we have demonstrated that the pollutants interacted to influence the response of radish (Raphanus sativus L.) foliage and root.

The influence of increasing O₃ concentrations at increasing concentrations of NO₂ and SO₂ generally resulted in smaller root (hypocotyl) fresh and dry weight, and in most cases the relationship was linear. Fresh-weight reductions in radish roots due to increasing O₃ concentrations from 0.1 to 0.2 ppm and from 0.1 to 0.4 ppm at 0.1 ppm NO₂ and SO₂ were 24 and 51%, respectively. At 0.4 ppm NO₂ and SO₂, the root-weight losses due to increasing O₃ concentration from 0.1 to 0.2 and from 0.1 to 0.4 ppm were 20 and 38%, respectively. When SO₂ reached 0.8 and 1.6 ppm, there was little change in root weight as NO₂ and O₃ concentrations were increased from 0.2 to 0.4 ppm. Nitrogen dioxide played a significant role in the response of radish to SO₂ and O₃, considering the high concentration of NO₂ (> 2.0 ppm) needed to cause a response in radish from a single exposure to NO₂ alone. These results suggested that valid assessment of the impact of siting additional sources of SO₂ and NO₂ in regions currently experiencing elevated O₃ levels will require recognition of this interaction potential.

Key Words: air pollutants • Raphanus sativus • pollutant interactions

¹ Cooperative investigations of the U.S. Dep. of Agriculture, North Carolina State University; and Advanced Fossil Energy Program, Environ. Sci. Div., Oak Ridge Natl. Lab. Research supported in part by the U.S. Dep. of Energy, Office of Health and Environ. Res., under contract W-7405-eng-26 with Union Carbide Corporation. Paper no. 6693 of the J. Ser. of the North Carolina Agric. Res. Service; and Pub. no. 1771, Environ. Sci. Div., Oak Ridge Natl. Lab., Oak Ridge, TN 37830.

² Plant Pathologist, Agric. Res., Sci. and Educ. Admin., USDA, and North Carolina State University, Raleigh, NC 27650; Ecologist, Environ. Sci. Div., Oak Ridge Natl. Lab.; and Professor of Statistics, North Carolina State University; respectively.

Received for publication December 17, 1980.