Biology and Fertility of Soils

, Volume 7, Issue 3, pp 275–278 | Cite as

Evaluation of nitrogen fixation by different strains of theAzolla-Anabaena symbiosis in the presence of a high level of ammonium

  • N. Okoronkwo
  • C. van Hovel
  • D. L. Eskew


The proportion of N derived from N2 fixation for 99 strains ofAzolla spp. (comprising all known species) in the presence of ammonium (40 mg/1) was assessed using a15N-dilution technique. The percentage of N derived from air varied from 29.5% to 79.9%. Although the N concentration ofAzolla spp. was not correlated with fertilizer N, it correlated fairly well with N2 fixation. Regression analysis suggests that the N yield ofAzolla spp. is more dependent on N2 fixation than on ammonium assimilation. The high correlation between N yield and isotopically determined, fixed N2 indicates that the N yield could be used as a parameter in the selection ofAzolla spp. strains that are capable of maintaining high N2 fixation in the presence of a high level of ammonium.

Key words

Ammonium assimilation Azolla spp. Dinitrogen fixation Productivity-N content N yield 15N dilution technique 


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Copyright information

© Springer-Verlag 1989

Authors and Affiliations

  • N. Okoronkwo
    • 1
  • C. van Hovel
    • 1
  • D. L. Eskew
    • 2
  1. 1.Laboratoire de Physiologic VégétaleUniversité Catholique de LouvainLouvain-la-NeuveBelgium
  2. 2.FAO/IAEA Agricultural Biotechnology LaboratorySeibersdorfAustria

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