Seedlings represent an important linkage for assessing the effect of air pollution on forests. This study examines the foliar responses of white ash seedlings to ozone and acid precipitation as a means of identifying atmospheric deposition effects on forests.

Significant differences were found among three red maple progenies in their height growth response to salt, to ozone and to salt and ozone combined. Seedlings from a Maine seed source showed the lowest degree of foliar injury in response to all treatments and were also least suppressed in their total height growth. Demonstrated genetic tolerance or susceptibility of red maple to ozone and salt supports the validity of selection programmes for trees capable of withstanding pollution-related stresses.

Height growth of silver maple, white ash, yellow-poplar, sycamore, eastern cottonwood, and white spruce seedlings was not significantly influenced by 0.15 ppM SO2 for 8 hours/day, 5 days/week. A fumigation treatment of 0.25 ppM SO2 for 8 hours/day, 5 days/week didn't significantly affect height growth of black alder, yellow-poplar, or white spruce seedlings but significantly reduced the height growth of eastern cottonwood, green ash, and sycamore seedlings. Exposure to toxic concentrations of SO2 (1 to 4 ppM) for 2 to 8 hours significantly affected the height growth and caused leaf injury in silver maple and yellow-poplar seedlings.

Positive correlations were established between morphological characteristics in eastern white pine seedlings and subsequent tolerance or sensitivity to air pollution 5 and 7 years after outplanting in Ohio plantations. Of 11 seedling variables, needle mottling was an accurate indicator of sensitivity or tolerance to air pollution. This characteristic, which may be genetically controlled, should allow for the detection and removal of sensitive white pines in the nursery during grading.

In the biosphere the biological components of aquatic and terrestrial ecosystems live in quasi-equilibrium. Air pollutants can produce changes in these biotic soil-water systems. To enhance the understanding of the impact of air pollutants on soil, water, flora, and fauna, this paper outlines the primary air pollutants, their sources, and their effects on biological systems. It also projects future trends in air pollutants and their ecological importance to the year 2000. 30 references.

These Proceedings report on the results of The First International Symposium on Acid Precipitation and the Forest Ecosystem which was held at The Ohio State University, Columbus, Ohio, U.S.A., on May 12-15, 1975. The Symposium focused on four related topics: (1) atmospheric chemistry, transport and precipitation; and effects of acidic precipitation on (2) aquatic ecosystems, (3) forest soils, and (4) forest vegetation.

The First International Symposium on Acid Precipitation and the Forest Ecosystem sponsored by the United States Department of Agriculture, Forest Service, Northeastern Forest Experiment Station, and by the Atmospheric Sciences Program of The Ohio State University was held in Columbus, Ohio, May 12-15, 1975. Approximately 300 people from 12 countries attended the Symposium.

Two-year-old white pine seedlings were sprayed one, two, or three times with 1- or 2- percent gibberellic acid and grown in photoperiods of 14 or 16 hr. Height growth increased significantly with additional foliar sprays, but was not affected by gibberellic acid concentrations or photoperiod. Forest Sci. 18:196-197.

Five-month-old seedlings of red maple (Acer rubrum L.) were fumigated with sulfur dioxide in a controlled environment for 4 or 6 hrs prior to measuring net photosynthesis. Concentrations of 6 ppm SO/sub 2/ caused acute foliar necrosis and resulted in depressed rates of photosynthesis. Plants fumigated at lower SO/sub 2/ levels (1 ppm) exhibited no foliar injury and showed a slight stimulation in CO/sub 2/ exchange when compared to unfumigated controls. Post fumigation recovery of maple seedlings exposed to 4.5 ppm SO/sub 2/ for 6 hrs was also studied. Net photosynthesis of SO/sub 2/-treated plants increased 88% during the 48 hr period following fumigation. This recovery occurred despite the gradual appearance of foliar damage on many of the treated seedlings. No correlation was found between the degree of stomatal opening and subsequent development of foliar symptoms in fumigated plants.

Coordinated research and action programs for reducing or preventing damage to forests from air pollution are briefly summarized. Program response to smelter pollution problems in southeastern Missouri are reviewed.