Comparison of Aluminon and 8-Hydroxyquinoline Methods in the Presence of Fluoride for Assaying Phytotoxic Aluminum
- A. D. Noble,
- M. E. Sumner and
- A. K. Alva
A nutrient solution study was conducted to evaluate the effects of varying pH (4.2, 4.5, and 4.8), Al (0, 20, 40, and 80 µM Al) and F- (0, 10, 20, and 40 µM F-) on soybean [Glycine max (L.) Merr. cv. Lee] root growth. The ability of Al fractions measured by the modified aluminon and 8-hydroxyquinoline methods in predicting the phytotoxic component of Al was also investigated. In the presence of Al up to 40 µM, increasing levels of F- resulted in an increase in root length. Aluminum speciation in solutions predicted by GEOCHEM program showed an increase in concentration of F- complexed Al species with an increase in concentration of F-. A very poor relationship was observed between tap root length and the sum of predicted concentrations of F- complexed Al species. Thus, F- complexed Al species would appear to be less phytotoxic than the other Al monomers. A highly significant correlation was found between tap root length and predicted concentration of Al3+ (R2 = 0.971). The relationship was further improved when sum of predicted concentrations of Al3+ and hydroxy-Al species was considered (R2 = 0.986). Tap root length was poorly correlated with the concentration of monomeric Al determined by the modified aluminon method, which included a larger portion of less phytotoxic F- complexed Al species. In contrast, a highly significant correlation (R2 = 0.984) was found between tap root length and the concentration of labile Al determined by the 8-hydroxyquinoline (15-s reaction) method. The labile Al may include only a very small fraction of F- complexed Al species. Therefore, in solutions containing varying concentrations of F-, Al measured by the 8-hydroxyquinoline (15-s reaction) method is a better predictor of Al phytotoxicity than that measured by the modified aluminon method.
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