The present volume developed from a symposium entitled "Enhancing Biological Production of Ammonia From Atmospheric Nitrogen and Soil Nitrate" that was held at Lake Tahoe, California in June, 1980. The meeting was supported by the National Science Foundation, Division of Engineering and Applied Sciences and by the College of Agricultural and Environmental Sciences, University of California, Davis. A total of 99 scientists from 41 insti tutions participated. Plants capture solar energy in photosynthesis and use mineral nutrients to produce human food and fiber products. The extent to which such materials are removed from agricultural production sites represents a permanent drain of mineral nutrients. Some plants of agronomic importance such as alfalfa, soybean, and clover associate with soil bacteria and use photosynthetic energy to reduce N2 to NH3. Many other free-living bacteria and some symbioses involving procaryotes and eucaryotes also reduce N2. Such processes repre sent one natural mechanism by which Man can augment soil N for agronomic purposes without using fossil fuel to synthesize and distribute N fertilizer. Other metabolic conversions in the N cycle and physical leaching processes remove N made available through N2 fixation. Thus nitrification, denitrification, and utilization of soil N by plants are processes that must be con sidered if one is to conserve N captured by N2 fixation. The meeting at Lake Tahoe united scientists from many disci plines to review the literature and to discuss current research directed toward the goal stated in the symposium title.

There is a time in scientific research when a number of developments coincide making it possible to progress with a tough and complicated problem. It is believed that such a time has come in the area of biological nitrogen fixation. A better understanding of photosynthesis, cell hybridization, plasmid, and gene transfer between cells not necessarily genetically related, have opened new avenues of research. New developments in traditional genetics, cell biology, biochemistry, including enzyme chemistry, and plant physi ology have brought about the feeling this is a most appro priate time to pull together the different approaches in a conference where the lines of research could be discussed and thus help to speed up developments in this area. What makes biological nitrogen fixation especially im portant is the promise that a good understanding of the basic problem would help us to make organisms more amenable to fix nitrogen, not only in symbiosis with legumes, but also with other plant species and develop a wider variety of organisms with the ability to fix N • It will also 2 encourage a search for naturally occurring N2 fixing organ isms other than the traditional N2 fixers. Some success has already been encountered in this area. Success in broadening the field of nitrogen fixing would help to increase food supply, especially in de veloping countries which cannot afford to purchase synthetic nitrogen sources.

A Seminar held in the Framework of the Biomolecular Engineering Programma of the Commission of the European Communities, at the Carlsberg Laboratory in Copenhagen, October 9-10, 1984

Phylogenetic classification of nitrogen-fixing organisms. Physiology of nitrogen fixation in free-living heterotrophs. Nitrogen fixation by photosynthetic bacteria. Nitrogen fixation in cyanobacteria. Nitrogen fixation by methanogenic bacteria. Associative nitrogen-fixing bacteria. Actinorhizal symbioses. Ecology of bradyrhizobium and rhizobium. The rhizobium infection process. Physiology of nitrogen-fixing legume nodules: compartments, and functions. Hydrogen cycling in symbiotic bacteria. Evolution of nitrogen-fixing symbioses. The rhizobium symbiosis of the nonlegume parasponia. Genetic analysis of rhizobium nodulation. Nodulins in root nodule development. Plant genetics of symbiotic nitrogen fixation. Molecular genetics of bradyrhizobium symbioses. The enzymology of molybdenum-dependent nitrogen fixation. Alternative nitrogen fixation systems. Biochemical genetics of nitrogenase. Regulation of nitrogen fixation genes in free-living and symbiotic bacteria. Isolated iron-molybdenum cofactor of nitrogenase.

The 14th International Nitrogen Fixation Congress was held in Beijing, China from October 27th through November 1st, 2004. This volume constitutes the proceedings of the Congress and represents a compilation of the presentations by scientists from more than 30 countries around the World who came to Beijing to discuss the progress made since the last Congress and to exchange ideas and information. This year marked the 30th anniversary of the first Congress held in Pullman, Washington, USA, in 1974. Since then, this series of Congresses has met five times in North America (three in the United States and once each in Canada and Mexico), once in South America (Brazil), four times in Western Europe (once each in Spain, The Netherlands, Germany and France), once in Eastern Europe (Russia), and once in Australia; and now for the first time in Asia. China was a most appropriate choice because China is a big country with the largest population in the World, about 1. 3 billion people, which is about 22% of the World’s population. It is traditionally an agricultural country, even though China has only 7% of the available farming land. This situation explains why agriculture and its productivity are major issues for the Chinese people, its government and the scientists in the field.