Joslin, J.D. and M.H. Wolfe. 1988. Responses of red
spruce seedlings to changes in soil aluminum in six amended
forest soil horizons. Canadian Journal of Forest Research,
Abstract: A greenhouse pot study was conducted to develop response curves for red spruce (Picea rubens Sarg.) seedlings to soil aluminum parameters, using soil from six diverse forest soil horizons. Soil A1 levels were manipulated by varying pH through acidification (with HC1 or HC1 and CaSO4), liming with Ca(OH)2), and control treatments. Treatments significantly (p < 0.05) altered soil pH (0.01 M CaCl2), 0.01 M SrCl2-extractable A1, and soil solution A1 concentrations. Root biomass and foliar biomass were significantly reduced in most acidification treatments, and strong correlations between soil parameters of A1 and biomass responses point to A1 as the major cause of biomass reductions, especially in the three horizons where the toxicity threshold (approximately 200 M inorganic monomeric A1) was markedly exceeded. Soil solution levels of inorganic monomeric A1 and total A1 (R2 = 0.79 and 0.74, respectively) were superior predictors of root biomass compared with the activity of A13+ in solution (0.61) and 0.01 M SrCl2-extractable A1 (0.61). Plant response curves to these soil solution inorganic monomeric A1 concentrations are in agreement with those developed in published research on solution culture of red spruce seedlings. Peak soil solution A1 concentrations measured in mature red spruce stands approach toxicity thresholds observed in this study.