Acid mist and soil Ca and Al alter the mineral nutrition and physiology ofred spruce

We examined the effects and potential interactions of acid mist and soil so lution Ca and Al treatments on foliar cation concentrations, membrane-assoc iated Ca (mCa), ion leaching, growth, carbon exchange, and cold tolerance o f red spruce (Picea rubens Sarg.) saplings. Soil solution Ca additions incr eased foliar Ca and Zn concentrations, and increased rates of respiration e arly in the growing season (July). Soil Al treatment had a broad impact, re ducing foliar concentrations of Ca, Mg, Mn, P and Zn, and resulting in smal ler stem diameters, sapling heights and shoot lengths compared with soil tr eatments with no added Al. Aluminum treatment also reduced respiration 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 withi n the range of sufficiency established for red spruce; (2) mCa concentratio ns were unaffected by Al treatment; and (3) no Al x Ca interactions were de tected. Acid mist treatment increased foliar Fe and K concentrations and in creased leaching of Ca, Mg, Mn, Zn, Fe, and Al from foliage. Leaching losse s of Ca were more than twice those of the element with the next highest amo unt of leaching (Zn), and probably led to the reductions in mCa concentrati on 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 treatment s, most involved the influence of mist pH and Al treatment on foliar nutrit ion. In general, reductions in cation concentration associated with Al addi tion were greater for pH 5.0-treated saplings than for pH 3.0-treated sapli ngs. We propose that H+-induced leaching of mCa from mesophyll cells is the mechanism underlying acid-induced reductions in foliar cold tolerance of r ed spruce.