The inorganic forms of Al in the soil solution that decrease plant growth in acid soils have not been clearly identified. Therefore, we examined the effects of Al and its complexes with F- and SO42- on the root elongation of barley (Hordeum vulgare) in nutrient solutions containing 3333 μmol Ca L-1 and 6 μmol B L-1 at pH 4.5. The anions were chosen because of their presence in the soil solution at levels sufficient to complex Al. The toxicity of 0 to 100 μmol Al L-1 was studied in the presence of 0 to 10 /μmol F L ' or 0-3300 μmol SO42 L-1. The elongation of roots of barley seedlings was correlated with Al3+ concentrations but not with total soluble Al or Al complexed with F and SO42-. This could be one of the reasons why measurements of labile Al using complexing agents have not always been successful at distinguishing between Al-toxic and nontoxic soils.
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