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  1. Vol. 17 No. 3, p. 443-445
     
    Received: Sept 7, 1976
    Published: May, 1977


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doi:10.2135/cropsci1977.0011183X001700030025x

Effects of Low Levels of Ozone on Growth of Crimson Clover and Annual Ryegrass1

  1. J. P. Bennett and
  2. V. C. Runeckles2

Abstract

Abstract

Studies have been conducted on short term exposure of plants to broad ranges of O3 concentration. Our purpose was to investigate long term exposure of plants to O3 levels that were below those normally causing visible injury. Annual ryegrass (Lolium multiflorum Lam.) and crimson clover (Trifolium incarnatum L.) were grown for 6 weeks in chambers within a greenhouse and fumigated for 8 hours/day with 0.03 and 0.09 ppm O3 in air. Treated plants showed less growth and yield than the controls despite the absence of visible injury. Both total dry weight and leaf area of treated plants were as much as 22% lower than the controls, but percent dry weight was significantly higher. Root growth was impaired the most, followed by stems and leaves, respectively, as evidenced by a lower root/shoot ratio and a slightly higher leaf weight ratio with O3 treatment. Both species showed significantly lower specific leaf areas and leaf area ratios in O3 compared to the control, but higher net assimilation rates led to relative growth rates which were unaffected. It was concluded that although the relative size of the leaf system was very sensitive to prolonged exposure to low O3, compensation in growth parameters occurred to counteract the stress response.

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