Summary We

examined the effects and potential interac-tions of acid mist and soil solution Ca and Al treatments on fo-liar cation concentrations, membrane-associated Ca (mCa), ion leaching, growth, carbon exchange, and cold tolerance of red spruce (Picea rubens Sarg.) saplings. Soil solution Ca addi-tions increased foliar Ca and Zn concentrations, and increased rates of respiration early in the growing season (July). Soil Al treatment had a broad impact, reducing foliar concentrations of Ca, Mg, Mn, P and Zn, and resulting in smaller stem diameters, sapling heights and shoot lengths compared with soil treat-ments with no added Al. Aluminum treatment also reduced res-piration when shoots were elongating in July and decreased net photosynthesis at the end of the growing season (September). Three lines of evidence suggest that Al-induced alterations in growth and physiology were independent of foliar Ca status: (1) Ca concentrations in foliage of Al-treated saplings were within the range of sufficiency established for red spruce; (2) mCa concentrations were unaffected by Al treatment; and (3) no Al × Ca interactions were detected. Acid mist treatment in-creased foliar Fe and K concentrations and increased leaching of Ca, Mg, Mn, Zn, Fe, and Al from foliage. Leaching losses of Ca were more than twice those of the element with the next highest amount of leaching (Zn), and probably led to the reduc-tions in mCa concentration and membrane stability of acid-treated saplings. Acidic mist resulted in enhanced shoot growth, and consistent reductions in foliar cold tolerance in the fall and winter. Of the few significant interactions among treat-ments, most involved the influence of mist pH and Al treatment on foliar nutrition. In general, reductions in cation concentra-tion associated with Al addition were greater for pH 5.0-treated saplings than for pH 3.0-treated saplings. We propose that H+-induced leaching of mCa from mesophyll cells is the mech-anism underlying acid-induced reductions in foliar cold toler-ance of red spruce