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Crop Science Abstract -

Effect of Salinity on the Functional Components of the Soybean-Rhizobium japonicum Symbiosis1


This article in CS

  1. Vol. 23 No. 5, p. 815-818
    Received: Dec 13, 1982

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  1. P. W. Singleton and
  2. B. B. Bohlool2



A split-root solution culture system was used to partition the effects of salinity on the functional components of the soybean [Glycine max (L.) Merr] - Rhizobium japonicum symbiosis. Nodules were confined to half of the root system. After nodules were well developed (40 days from planting), 120 mM NaCl was applied to the half-root systems in the following combinations: 1)unstressed, no salt to either half-root system; 2) partially stressed shoot and unstressed nodules, salt to only the nonnodulated halfroot system; 3) partially stressed shoot and stressed nodules, salt to only the nodulated half-root system; and 4) stressed shoot and nodules, salt to both half-root systems. Leaf osmotic potentials (ψs) for the four treatments were: 1) −1.02; 2) −1.12; 3) −1.23; and 4) −1.83 MPa. Nodule ψs for the treatments were: 1) −0.70; 2) −0.72; 3) −1.12; and 4) −1.21 MPa. While total and specific nitrogenase activity as well as shoot N content were suppressed in treatment 3, the greatest decrease in activity and shoot N was observed when the plant was stressed by having both half-root systems in salt (treatment 4). The rate of leaf expansion in treatment 4 was half the rate observed in the other treatments. We conclude that reduced N2 fixation by nodulated soybeans growing in saline environments was more a result of the effect of salt on leaf ψs and expansion, than the direct action of salt on the functional processes of the nitrogenase system.

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