Differential tolerances of two old world bluestem genotypes to excess aluminum in acid soil and nutrient solution

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Abstract
Two genotypes of Old world bluestems from the species Bothriochloa intermedia (R. Br.), A. Camus, shown earlier to differ in tolerance to acid, Al‐toxic Tatum subsoil at pH 4.1, were characterized further with respect to growth in pots of Tatum soil over a wider pH range and tolerance to Al in nutrient solutions. The two genotypes studied were acid‐soil tolerant P. I. 300860 (860) and acid soil sensitive P. I. 300822 (822). The soil experiment confirmed earlier rankings of acid soil tolerance in these two genotypes. For example, with 0, 375 or 750 ug CaCO3 g‐1 soil (final pH 4.0, 4.3 and 4.6), the 860 genotype produced significantly more dry top weight than 822, but these differences were precluded with 1500 or 3000 ug g‐1 CaCO3 added (pH 4.7 and 5.4). At pH 4.3 and 4.6, the root dry weights of the two genotypes were also significantly different and weights were equalized at pH 4.7 and 5.4. The 860 genotype made fairly good top growth (67% of maximum) at pH 4.3 and a soil Al saturation of 63%; this situation was lethal for 822. When grown in greenhouse pots, the acid‐soil tolerant 860 genotype required only about one fourth as much CaCO3 as 822 to produce good growth of forage on acid Tatum subsoil. If confirmed under field conditions, such a difference could be economically significant in reclaiming acidic marginal land and in producing forage at low cost. Differential Al tolerance in the two genotypes was confirmed in nutrient solutions. For example, with 8 mg Al L‐1 added, both top and root dry weights of 860 were significantly higher than those of 822, but with no Al added, these growth differences disappeared. Mineral analyses of plants did not shed much light on mechanisms of differential acid soil or Al tolerance. For example, Al concentrations in plant tops associated with toxicity varied from 33–43 ug g‐1 in nutrient solutions containing Al to 119–283 ug g‐1 in acid soil It appears that elucidation of Al‐adaptive mechanisms will require physiological and biochemical studies at the cellular level.