Aluminum Toxicity, Nodulation, and Growth of Stylosanthes Species
1981
de Carvalho, Margarida M. | Edwards, D. G. | Andrew, C. S. | Asher, C. J.
Aluminum toxicity is an important limitation to legume growth on many acid soils. Stylosanthes species are often grown on such soils, but effects of A1 on their growth are poorly understood. Effects of four solution A1 concentrations (0, 25, 75, and 125 µM) on the growth of six Stylosanthes species was examined on plants supplied with 500 µM NH₄NO₃ and on plants inoculated with Rhizobium CB 756. Aluminum toxicity depressed growth more severely in those plants dependent on symbiotic N₂ fixation than in those supplied with combined N. At 25 µM Al, S. hamata (L.) Taub. and S. fruticosa (Retz) Alston exhibited high tolerance when dependent on symbiotic N₂ fixation, while the other four species were less tolerant. Yield of all six species was strongly depressed at 125 µ Al, irrespective of the N source. The greater sensitivity of the inoculated plants to A1 toxicity was associated with a strong reduction in nodulation f all species. Aluminum delayed nodulation in all species except S. hamata, reduced the number of plants which nodulated in S. guianensis (Aubl.) Sw., S. scabra Vog., and S. viscosa Swartz, and reduced the number and dry weight of nodules in all six species. Greater effects of A1 on nodule weight than on root weight were observed particularly in the more poorly nodulated species S. guianensis, S. scabra, and S. viscosa. Tolerance to Al by the various species thus appears to be dependent on their ability to nodulate and develop an effective symbiosis in the presence of Al, and on the inherent sensitivity of the host plant to Al.
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