Ozone impacts on seasonal foliage dynamics of young loblolly pine
1992
Stow, T.K. | Allen, H.L. | Kress, L.W.
Effects of above- and below-ambient levels of ozone (O3) on the production, abscission, and duration of foliage of young loblolly pine (Pinus taeda L.) grown in open-top chambers were examined in the Piedmont of North Carolina. Assessments of fascicle elongation and number were made at frequent intervals during 1988, 1989, and 1990 for all 1988 primary flushes on the stem and at a branch position. Ozone treatment had little effect on overall foliage production; however, all elevated O3 levels reduced foliage retention. Foliage abscission for most flushes was initiated when cumulative O3 dose exceeded 130 to 220 ppm-hr regardless of crown position for trees exposed to ambient and above-ambient O3 levels. Reductions in leaf area duration of the 1988 cohort were observed at ambient and higher O3 levels. Total leaf area duration was 22 and 25% greater for the stem and branch positions in the charcoal-filtered as compared to nonfiltered treatments. The greater duration in charcoal-filtered chambers resulted from significantly greater retention into the third growing season. Foliage development and ozone responses at the branch position were more representative of the whole crown than those at the stem position.
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