Differential Aluminum Tolerance of Two Wheat Varieties Associated with Plant‐Induced pH Changes Around Their Roots

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Differential Al tolerance of Atlas 66 and Monon wheat varieties in nutrient solutions and in acid Bladen soil was attributed, at least in part, to plant‐induced differential pH changes around their roots. In nutrient solutions the Al‐sensitive Monon variety lowered the pH and the Al‐tolerant Atlas variety raised the pH, resulting in differences as large as 0.7 pH unit in the nutrient media. In acid Bladen soil this difference was much smaller, and a high root‐to‐soil ratio was necessary to produce observed pH differences that were significant. The factor responsible for higher Al‐tolerance of Atlas was not transferred to Monon in mixed cultures in Bladen soil. The evidence indicates that the layer of plant‐altered soil surrounding the roots was extremely thin.