Patterns of ammonium absorption and acetylene reduction during soybean developmental growth

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Abstract
Nodulated and unnodulated soybean plants (Glycine max (L.) Merr. cv. Amsoy 71) were grown in nutrient solution either lacking or containing N. Nodulated plants, dependent on N2 fixation, exhibited a generalized N‐stress and were less vigorous than unnodulated plants dependent on inorganic N assimilation.Starting at preflowering throughout mid pod‐filling, NH4+ absorption, expressed on the basis of root dry weight, was determined for intact nodulated and unnodulated plants in short‐term kinetic experiments. Depletion of NH4+ was measured from the liquid phase of a mist chamber. Maximum NH4+ absorption occurred for both nodulated and unnodulated plants during vegetative growth. A pattern of progressive decrease in NH4+ absorption was similar in nodulated and unnodulated plants, however. NH4+ absorption was consistently greater in unnodulated plants. Simultaneous measurements of C2H2 reduction from the gas phase of the mist chamber revealed and 41‐day‐old plants, corresponding to late flowering and early pod‐filling.