Response of northern red oak (Quercusrubra) seedlings to soil solution aluminum

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Abstract
The sensitivity of northern red oak (Quercusrubra L.) to soil solution Al was experimentally examined on germinants grown for 10 weeks in a soil sample from the B2/C horizons of a Typic Fragiorthod. Adding AlCl3 raised the solution Al in the saturated paste extract from about 50 to 825 μM in study I and to 392 μM in study II. Phosphorus (KH2PO4) was added in study II. Forty percent of the variation in root growth was related to solution Al, even in study I where severe P deficiency dampened the expression of Al toxicity. Shoot growth was less sensitive to Al. In study II, total root weight was significantly reduced (36%) at 115 μM Al. This is the lowest concentration of Al reported to significantly reduce seedling growth of oak. The Ca and Mg concentrations in leaves and roots were first reduced at 115 μM Al. Higher solution Al further reduced these to levels associated with deficiency in other dicotyledonous trees. Tissue Al concentrations were not closely correlated with growth.