Seedling Responses of Five Species of Western Conifers to Simulated Ambient Sulfur Dioxide Exposures

Abstract

Abstract Seedlings of ponderosa pine, Douglas-fir, white fir, Engelmann spruce, and subalpine fir were exposed continuously to charcoal-filtered (CF) air or one of three levels of a simulated ambient exposure typical of SO2 pollution near smelters in the western United States. Seedlings were exposed during winter-spring experiments for 60 days to hourly means of 17, 38, and 54 ppb in 1988 and 35, 57, and 99 ppb in 1989. Sensitivities of species to SO2 were determined from height growth, diameter growth, root, stem, and needle weights, and from foliar injury. Ponderosa pine in all SO2 treatments in 1989 had decreased diameter growth and decreased needle weights compared with those in CF air. In 1989, average diameter growth of Douglas-fir in all SO2 treatments was less than those in CF air. Diameter growth and needle weights of ponderosa pine were correlated in all SO2 treatments and CF air. Diameter growth and needle weights of Douglas-fir were correlated in all SO2 treatments. Tip necrosis of needles occurred on a larger proportion of seedlings of all species in high SO2 than on those in CF air. Ponderosa pine and Douglas-fir were about equally sensitive to SO2 and both were more sensitive than white fir. White fir was more sensitive to SO2 than Engelmann spruce and subalpine fir which were equally unresponsive to SO2. For. Sci. 37(6):1538-1549.