Modeling the potential for boron amelioration of aluminum toxicity using the Weibull function

Several recent reports have suggested that boron (B) may alleviate the toxic effects of aluminum (Al) on plant growth, providing improved plant performance on acid soils. To test this hypothesis, an Al-sensitive cultivar of Triticum aestivum L. (cv. Neepawa) was grown in solution culture with 10 concentrations of Al (0–300 μM), in the presence of deficient (0 μM), sufficient (6 μM), luxury (75 μM), or toxic (750 μM) concentrations of B. The effects of both Al and B on the response of roots and leaves to Al was accurately modeled (R2 < 0.99) using a modified Weibull function. Comparison of best fit function parameters for the response to Al under varying conditions of B supply failed to reveal any evidence of B amelioration of Al toxicity. The combined effects of Al and B were adequately explained by a multiplicative model. Although formation of stable Al-borate complexes could occur in growth solutions under our experimental conditions, varying the supply of B had little effect on accumulation of Al in roots and leaves. In contrast, increasing Al concentrations in solution resulted in increased immobilization of B in roots and decreased accumulation of B in leaves. Growth of plants with elevated B supply resulted in higher concentrations of B in roots and leaves without improving growth. We suggest that previous reports of B amelioration of Al toxicity must reflect the unique characteristics of soil-based media, and (or) differences among species in internal requirements for B and the effects of Al on B nutrition.