Role of root cation‐exchange capacity in differential aluminum tolerance oflotusspecies

Abstract

Abstract Three experiments were conducted in which roots of two species of Lotus were immersed for up to 40 min in complete nutrient solutions containing 6, 15 or 25 μM Al. The two species tested were L. pedunculatus cv. Grasslands Maku (Al‐tolerant) and L. corniculatus cv. Maitland (Al‐sensitive). There was an initial rapid (< 5 min) decrease in solution Al at 25 μM Al. The effect was less marked with solution Al ≤ 15 μM. The decrease in solution Al was greater in the Al‐sensitive Maitland than in the Al‐tolerant Grasslands Maku, particularly when expressed on the basis of root fresh mass and root length. Root cation‐exchange capacity (CEC) was lower in Grasslands Maku than in Maitland, viz. 23.9 vs 36.5 mmol kg‐1 dry mass. Maitland roots removed more Al from solution than did those of Maku on the basis of total exchange capacity. We propose a mechanism of Al tolerance on the basis of the results of this study and of other published information, viz. that differential Al tolerance results from difference...