The Effect of pH, Temperature, and \(N{O_3}^ - \) Concentration on \(N{H_4}^ + \) Absorption and N2(C2H2)-Fixation by Soybeans

  • Lynn Marcus-Wyner
  • D. W. Rains


Nodulated and nonnodulated soybeans (Glycine max (L) Merr., Amsoy 71) were supplied with complete nutrient solution either lacking or containing nitrogen. Intact plants, at the flowering stage were transferred from solution culture to a mist assay chamber. In this chamber plant roots were sprayed with an uptake solution ranging from 0.05 to 1.0 mM NH4Cl and 0.5 mM CaSO4. Concurrently root nodules were exposed to 0.12 ml/ml C2H2. Simultaneous measurements were made for NH4+ absorption and C2H2 reduction.

The short-term uptake pattern for NH4 resembles a hyperbolic curve. Uptake was linear for over 6 hours, except for an initial rapid uptake period. Ammonia absorption capacity was consistently greater in uninoculated plants than in inoculated plants. Varying the pH range of experimental solutions from 4.0 to 6.8 did not significantly influence NH4+ uptake in nodulated plants, but had a stimulatory effect in nonnodulated plants. Short-term exposure to lower pH levels did not alter acetylene reduction rate.

When 0.1 to 2.0 mM KNO3 was added to uptake solutions NH4+ absorption was not significantly influenced in either nodulated or nonnodulated plants. In addition, pretreatment of plants for 16 hours with 0.5 mM KNO3 and 0.5 mM NH4C1 did not change the absorption rate. Acetylene reduction rate decreased when nodulated plants were pretreated with nitrogen, but reduction rate did not change when plants were exposed to varying NO3 concentrations for short time periods. When the temperature of the uptake solution was decreased from 28 to 22 C acetylene reduction rate also decreased, but NH4+ absorption rate did not significantly change in either nodulated or nonodulated plants.

In general, it appears that neither process NH4+ absorption nor acetylene reduction is very sensitive to the short-term environmental changes in our mist system. Acetylene reduction is more sensitive to temperature changes and NH4+ is more sensitive to pH changes.


Absorption Rate Solution Culture Flower Stage Intact Plant Acetylene Reduction 
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Copyright information

© Plenum Press, New York 1981

Authors and Affiliations

  • Lynn Marcus-Wyner
    • 1
  • D. W. Rains
    • 1
  1. 1.Department of Agronomy & Range ScienceUniversity of CaliforniaDavisUSA

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