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Acidity and Aluminum Restraints on Nodulation, Nitrogen Fixation, and Growth of Phaseolus vulgaris in Solution Culture¹

ABSTRACT

The effects of acidity and aluminum (Al) on nodulation, nitrogen (N) fixation, and bean shoot and root growth were studied in solution and sand culture in greenhouse experiments to help explain the frequent failure of N₂-dependent bean in acid soils. Aluminum concentrations were maintained in solution by keeping low levels of phosphorus (P) at pH 4.5.

Concentrations of Al up to 83 µM did not affect root dry weight, nodule growth, and nitrogenase activity of either bean cultivar tested. Low levels of Al (19 µM) increased taproot elongation but decreased total root length; at higher Al concentrations, the taproot also became stunted. Increasing CaCl₂ from 0.2 to 2 mM in solution suppressed Al toxicity. Shoot growth was significantly decreased by 19 µM Al in P. vulgaris cv. Carioca but not in cv. Venezuela 350. Root colonization and/or infection by Rhizobium was reduced by Al concentrations >33 µM but was less sensitive than total root elongation or shoot growth.

Solution culture pH in the range 4.5 to 5.5 did not affect nodule growth and nitrogenase activity, but a decrease in pH from 5.5 to 5.0 decreased number of nodules formed per plant from 60 to 10, indicating that pH can be a major limiting factor of early nodulation with the cultivars and Rhizobium strains tested.

¹ Contribution from Dep. of Land, Air and Water Resources (LAWR), Univ. of California, Davis CA 95616.

² Researcher, Empresa Brasileira de Pesquisa Agropecuaria—SNLCS—PFBN, 23460, Seropedica, Rio de Janeiro; and Professor, LAWR, Univ. of California, Davis.

Received for publication June 29, 1981. Accepted for publication September 21, 1981.