Biological fixation of nitrogen by organisms and associations other than those concerned in the legume-Rhizobium symbiosis has attracted increasing attention since the firstintemationalworkshop on the theme at Piracicaba, Brasil, in 1979. Approximately 150 scientists gathered on September 2-8, 1984, at the Hanasaari Cultural Centre near Helsinki, Finland, for the third international meeting on nitrogen fixation with non-legumes. Forty-two papers and 39 posters were presented; 32 of the papers have been broughttogetherin this publication. The Symposium was generously sponsored by the FinnishNational Fund for Research and Development (SITRA) in connection with a large project on biological nitrogenfixation and utilization ofnitrogen extending from 1980 to 1985. The Symposium was organized jointly by SITRA, which dealt with all practical matters very efficiently and with impressive concern for the welfare of the participants, and Societas Biochemica, Biophysica et Microbiologica Fenniae, the society of Finnish microbiologists, which made valuable contributions on scientific matters. As in the previous symposium at Banff, Canada, in 1982 the programme did not involve parallel sessions~ all participants had the opportunity of listening to all presentations. Consequently, the FIN- NIF Symposium profited from a steady audience and the consistency this gave to the discussions. In view of the growing interest in N-fixation with non-legumes and the continuous broadening of the field, such an arrangement may not be possible in the future. I thank all participants for their contributionsto both oral sessions and poster presentations, and hope that this publication will become a frequently quoted source of knowledge.

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The Third International Symposium on Nitrogen Fixation with Non-Legumes, Helsinki, September 2-8, 1984

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Session 1: Biology of interactions between plants and diazotrophic bacteria.- Development and function of Azospirillum-inoculated roots.- Lichens to Gunnera with emphasis on Azolla.- Establishment of inoculated Azospirillum spp. in the rhizosphere and in roots of field grown wheat and sorghum.- Effects of oxygen partial pressure and combined nitrogen on N2-fixation (C2H2) associated with Zea mays and other gramineous species.- Adhesion of fimbriated nitrogen-fixing enteric bacteria to roots of grasses and cereals.- Session 2: Microbial ecology of diazotrophic bacteria.- Ecological factors, and adaptive processes in N2-fixing bacterial populations of the plant environment.- Nitrogen fixation associated with roots of Kallar grass (Leptochloa fusca (L.) Kunth).- Growth and survival of Azospirillum brasilense and Arthrobacter giacomelloi in binary continuous culture.- Population dynamics of Azospirillum brasilense and its bacteriophage in soil.- Chemotaxis of free-living nitrogen-fixing bacteria towards maize mucilage.- Utilization of simple phenolics for dinitrogen fixation by soil diazotrophic bacteria.- Enrichment of diazotrophic bacteria from rice soil in continuous culture.- Session 3: Biochemistry and physiology of nitrogen fixation.- Biochemistry and physiology of nitrogen fixation with particular emphasis on nitrogen-fixing phototrophs.- Aspects of nitrogen fixation and denitrification by Azospirillum.- Studies of the adenylate and pyridine nucleotide pools during nitrogenase 'switch-off' in Rhodospirillum rubrum.- Shifts in the intracellular ATP pools of immobilized Nostoc cells (Cyanobacteria) induced by water stress.- Session 4: Genetics of nitrogen fixation.- Regulation of the nitrogen fixation genes in Klebsiella pneumoniae: Implications for geneticmanipulation.- Cloning of pEA3, a large plasmid of Enterobacter agglomerans containing nitrogenase structural genes.- Session 5: Methods of measuring nitrogen fixation.- The role of root-associated Klebsiella pneumoniae in the nitrogen nutrition of Poa pratensis and Triticum aestivum as estimated by the method of 15N isotope dilution.- Use of isotope dilution to measure nitrogen fixation associated with the roots of sorghum and millet genotypes.- Estimation of biological nitrogen fixation associated with Brachiaria and Paspalum grasses using 15N labelled organic matter and fertilizer.- Evaluation of the availability of Azolla-N and urea-N to rice using 15N.- Session 6: Nitrogen fixation by non-legumes in agriculture.- Nitrogen fixation associated with non-legumes in agriculture.- Effect of Azosprillium inoculation on nitrogen fixation and growth of several winter legumes.- Nitrogen fixation by non-legumes in tropical agriculture with special reference to wetland rice.- Laboratory acetylene reduction assay for relative measurement of N2-fixing activities associated with field-grown wetland rice plants.- Effect of seed inoculation, mycorrhizal infection and organic amendment on wheat growth.- Effect of incorporation of crop residues on development of diazotrophs and patterns of acetylene-reducing activity in Nile Valley soils.- Session 7: Nitrogen fixation by non-legumes in forestry and natural ecosystems.- The improvement and utilization in forestry of nitrogen fixation by actinorhizal plants with special reference to Alnus in Scotland.- Distribution of Frankia in soils from forest and afforestation sites in northern Sweden.- Nitrogen fixation in coniferous bark litter.- Closing session.- The genetics of actinorhizal Frankia: A review.- Titles of posters presented at the meeting.- Videotape presentation (Session 2).- Index of keywords.