GROWTH AND WATER RELATIONSHIPS OF RED SPRUCE SEEDLINGS EXPOSED TO ATMOSPHERIC DEPOSITION AND DROUGHT

Two-year-old containerized seedlings of red spruce (Picea rubens Sarg. ) were subjected to ozone (O3) fumigation (0.25 ppm), simulated acid r ain (pH 4.2 or 3.0), and drought prior to measurement of changes in gr owth and plant water status. Drought caused a significant decline in t erminal height growth and new-shoot dry weight, but old-shoot dry weig ht, root dry weight, and root/shoot ratio were not appreciably affecte d. Deposition treatment (O3 and (or) acid rain) influenced both shoot and root dry weight but did not significantly affect height or root/sh oot ratio. Treatment with either 0.25 ppm O3 alone or pH 3.0 rainfall alone caused the greatest reduction in growth, while treatment with 0. 25 ppm O3 + pH 4.2 rain had the least effect. The influence of deposit ion treatment generally was more pronounced in seedlings subjected to drought than in well-watered plants. Seedlings subjected to drought ha d lower (more negative) water potentials than well-watered plants rega rdless of deposition treatment. While there were no significant differ ences in the water status of well-watered seedlings exposed to various deposition treatments, xylem water potential and osmotic potential of drought-stressed seedlings treated with O3 alone were consistently lo wer than these characteristics in seedlings treated with O3 + acid rai n together. Except for one deposition treatment (0.25 ppm O3 + pH 3.0 rain) there was no evidence for osmotic adjustment of red spruce seedl ings in response to stress factors imposed in this study.