Air pollutants affect the relative growth rate of hardwood seedlings

Abstract

One-year-old seedlings of yellow-poplar (Liriodendron tulipifera L.), eastern cottonwood (Populus deltoides Bartr.), and white ash (Fraxinus americana L.) were divided into four groups. One group served as the control, and the other groups were fumigated for 12 hours per day with either 0.1 ppm O3, 0.2 ppm SO2, or 0.1 ppm O3 plus 0.2 ppm SO2. Two or three seedlings of each species were harvested twice a week for 6 weeks, and leaf area and new growth weight were determined. Data on leaf area and new growth weight were transformed to natural logarithms and fitted with a linear regression model. Relative growth rate was positive in all species-treatment combinations, but varied with fumigation treatment. Net assimilation rate was suppressed in cottonwood seedlings in all fumigation treatments, and in yellow-poplar seedlings in the SO2 and O3 fumigations. Relative leaf area growth rate of the cottonwood and yellow-poplar seedlings was reduced by all three fumigation treatments. White ash growth was not analyzed because statistically significant differences were not found.