Effect of Salinity on the Functional Components of the Soybean-Rhizobium japonicum Symbiosis1
- P. W. Singleton and
- 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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