Phenology and cold tolerance of Picea rubens Sarg. seedlings exposed to sulfuric and nitric acid mist

During the growing seasons of 1985-88, red spruce (Picea rubens Sarg.) seedlings were exposed repeatedly in field chambers to sulfuric and/or nitric acid mist in the range of pH 2.5 to 4.5. Hydrogen ion, sulfate, and nitrate concentrations in mist were within the range found in cloudwater of the northeastern USA where high-elevation spruce forests are declining. After the period of exposures, seedlings remained outdoors and buds were sampled in the autumn to determine effects of mist treatments on the number of developing needle primordia. Current-year foliage was sampled from autumn to spring for measurement of cold tolerance by freeze-induced electrolyte leakage (FIEL) and buds were scored for degree of bud break in the early spring. In the 1985-87 experiments when 16-hour overnight mist events were continuous, there were few statistically significant effects of acidic mist on needle primordia development, foliar FIEL, and bud-break. However, in the 1988 experiment when 16-hour overnight mist events were in intermittent rather than continuous and acidities fluctuated among events, sulfuric acid mist decreased the number of needle primordia in September and October relative to the other treatments. Acidity of mist increased FIEL in October. Sulfate and nitrate content of mist appeared to influence these effects of acidity on FIEL differently depending on level of cold tolerance and duration of time since the period of exposure to mist. Bud-break in May was not significantly affected by prior mist treatments. Responses to acidic mist were similar among provenances that obtained from different locations in the northeastern USA, although provenances differed in phenological development and FIEL. Mist deposition to the soil medium was minimized or avoided in these experiments; therefore, we concluded that foliar FIEL of red spruce seedlings is vulnerable to effects of direct contact of acidic mist with foliage. To relate results of these controlled experiments to cloudwater and decline of red spruce trees in the northern Appalachian mountains, the following information is needed: the frequency of wet-dry cycles in the forest; fluctuations in acidity and sulfate and nitrate concentrations among and within cloudwater events; the specific patterns of temperature changes that lead to winter injury; and the relationship between FIEL and freezing damage to foliage for both seedlings and mature trees.