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This article in SSSAJ

  1. Vol. 30 No. 1, p. 56-60
    Received: July 12, 1965
    Accepted: Sept 17, 1965

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Fixation of Isotopic Nitrogen on a Semiarid Soil by Algal Crust Organisms1

  1. H. F. Mayland2,
  2. T. H. McIntosh and
  3. W. H. Fuller3



Semiarid desert algal crust organisms were found to fix N2 when exposed to an atomosphere which contained isotopically enriched N. Significant quantities of the N isotope were detected in the total crust N after 3 days of incubation under field-simulated conditions.

Net N2 fixation rates by the algal crust organisms were 0.16 and 0.10 lb of N/acre of crust surface per day under continuous wet and cycling wet-dry conditions, respectively. Net fixation of N under field-simulated conditions adequately compensated for the removal of N by livestock. The rate of N2 fixation under field-simulated conditions increased linearly for at least 520 days. The amount of N in the algal crust was doubled during this time. No net N change was observed in dry crusts.

Growing algal crusts contained 1% to 2% of the total N as extracellular NH4-N. Excretion of some fixed nitrogen was suggested by the isotopic enrichment of the extracellular N fraction and uptake of labeled N by grass seedlings (Artemesia sp.) growing on incubated crusts.

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