Growth response of two varieties of slash pine seedlings to chronic ozone exposures

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Abstract
Two geographical varieties of Pinus elliotii (Engelm.) seedlings, elliottii and densa, were exposed continuously to two daily peak exposure profiles of ozone having 7-h (0900-1600) seasonal means of 0.104 and 0.076 ppm and charcoal-filtered air over a 112-day period. The profiles represented a daily rise and decline of hourly ozone concentration. They were constructed with a daily hourly maximum, which for one profile (0.126 .mu.L/L) exceeded the current ozone standard daily; the standard was not exceeded for the other profile (0.094 .mu.L/L). Destructive harvests at 7-day intervals over the exposure period were employed to assess visible injury and to construct growth curves for stem diameter, plant height, top and root dry weight, and needle number and length. The visible injury was slight, yet all the growth parameters decreased significantly with time and ozone concentration; root growth was the most severely impacted. The observed growth response and visible injury of the two varieties were similar. Seed germination was not affected by ozone exposure.