EFFECTS OF ALUMINUM, OH

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Abstract
The effects on soybean root length after 4 days'' growth in nutrient solutions approximating soil solutions were studied. Additions of NaOH and NaH2PO4.cntdot.2H2O solutions decreased the concentrations of monomeric Al species in solution, Al polymers being formed with Al concentrations .ltoreq. 50 .mu.M originally in solution but not at concentrations .gtoreq. 100 .mu.M Al. In nutrient solutions with ionic strengths .ltoreq. 900 .mu.M, the Al polymers formed remained in solution, but were not detected in solutions with higher ionic strengths. Soybean root elongation was reduced severely with Al concentrations of .gtoreq. 10 .mu.M. The toxic effectof Al was ameliorated by the addition of OH or P through the reduction of monomeric Al species in solution. A close curvilinear relationship was observed between relative root length (%) (y) and .SIGMA. activities (.mu.M) of the monomeric Al species in solution (x) (y = 14.9972 + 99.163 exp(-0.130605x); R = 0.950***), irrespective of the intial Al concentration, the concentration of polymeric Al species in solution, ionic strength, solution nutrient composition, P concentration, or pH. One or more of the monomeric Al species apparently was responsible for the toxic effect of Al on soybean root growth; the ameliorating effect of OH and P probably resulted from the reduction in the concentration of monomeric Al in solution, either through polymerization or precipitation of Al.