RESPONSES OF KENTUCKY BLUEGRASS CULTIVARS TO EXCESS ALUMINUM IN NUTRIENT SOLUTIONS

Kentucky bluegrass, Poa pratensis L., is generally regarded as an acid -soil-sensitive species. However, previous studies in our laboratory s howed that cultivars within the species differed widely in tolerance t o acid Tatum subsoil (pH 4.6) which is used routinely to screen plants for aluminum (Al) tolerance. In the early studies, specific different ial Al tolerance was not demonstrated. The objective of the current st udy was to test the hypothesis of differential Al tolerance more preci sely in nutrient solutions. In one experiment, acid-soil-tolerant Vict a and Fylking and acid-soil-sensitive Windsor and Kenblue cultivars we re grown for 35 days in nutrient solutions containing 0, 2, 4, 6, 12, and 24 mg Al L-1, at initial pH 4.5, with no subsequent adjustment. In a second experiment, Victa and Windsor were grown for 30 days in solu tions containing 0, 4, and 6 mg Al L-1, at initial pH 4.5, with no fur ther adjustment. For Victa and Windsor, tolerance to Al in nutrient so lution corresponded with tolerance to acid Tatum subsoil, however, the cultivar difference in tolerance, based on relative root dry weight, was only about 2-fold, compared with 20-fold in acid Tatum subsoil. Fy lking and Kenblue cultivars, which showed a wide difference in toleran ce to acid Tatum subsoil, did not show distinct differences in toleran ce to Al in nutrient solutions. Possible reasons for this discrepancy are discussed. Superior Al tolerance of Victa (compared with Windsor) was associated with a greater plant-induced increase in the pH of its nutrient solutions and a corresponding decrease in concentrations of s oluble Al in the filtered solutions at the end of the experiments. Gre ater Al sensitivity in Windsor (compared with Victa) was not related t o reduced uptake of phosphorus (P) or excessive uptake of Al; neither cultivar accumulated appreciable Al concentrations in its shoots. The observed differential acid soil and Al tolerance among bluegrass culti vars appears worthy of further study. Improved understanding of Al tol erance mechanisms would contribute to fundamental knowledge of plant m ineral nutrition and could aid plant breeders in tailoring plants for greater tolerance to acid subsoils.