Plant Physiol. Drug Metab Dispos
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Plant Physiology 69:460-464 (1982)
© 1982 American Society of Plant Biologists

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Articles

Simultaneous Measurement of NH4+ Absorption and N2 Fixation by Glycine max L. 1

RESPONSE TO TEMPERATURE, pH, AND EXTERNAL NITROGEN CONCENTRATION

Lynn Marcus-Wyner2 and D. William Rains

Department of Agronomy and Range Science, University of California, Davis, California 95616

Ammonium absorption rates by intact nodulated and unnodulated soybean plants (Glycine max [L.] Merr., Amsoy 71) were determined from the liquid phase of a mist assay chamber. From the gas phase, simultaneous measurements of acetylene reduction rates were made from nodulated plants. Ammonium absorption capacity was consistently greater in unnodulated plants.

At the beginning of flowering, plant roots were sprayed with an uptake solution ranging from 0.05 to 1.0 millimolar NH4Cl, and root nodules concurrently were exposed to 0.12 atmosphere acetylene. The NH4+ absorption system of both nodulated and unnodulated plants were nearly saturated at 0.3 to 0.5 millimolar NH4+.

Increasing the pH from 4.0 to 6.8 stimulated NH4+ absorption rate in both flowering and preflowering nodulated and unnodulated plants. Acetylene reduction rate was not altered by short-term exposure to increased acidity. Short-term exposure to lower absorption solution temperatures from 32°C to 18°C did not significantly affect NH4+ absorption rate in flowering nodulated or unnodulated plants. However, acetylene reduction rate increased as the absorption solution temperature increased. The Q10 value was 1.5 for the reaction rate. Increasing external NO3– concentration from 0.1 to 5.0 millimolar NO3– did not significantly influence the kinetics of NH4+ absorption or acetylene reduction rate.

2 Present address: Department of Plant and Soil Sciences, University of Massachusetts, Amherst, MA 01003.

1 This material is based on research supported by National Science Foundation Grant AER 77-07301.






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ASPB Publications PLANT PHYSIOLOGY THE PLANT CELL
Copyright © 1982 by the American Society of Plant Biologists