These proceedings bring together diverse disciplines that study nitrogen fixation and describe the most recent advances made in various fields: chemists are now studying FeMoco, the active site of nitrogenase in non-protein surroundings, and have refined the crystal structure of the enzyme to 1.6 angstroms.

The refinement of molecular techniques and the development of new probes of the phylogeny of diazotrophs has revealed an extreme biodiversity among the nitrogen fixers, which helps explain the role that nitrogen fixation plays in maintaining life on Earth. The most efficient ecosystems are those where the bacteria are associated with a plant in differentiated organs to benefit crop productivity. Most short-term benefit from fundamental research on nitrogen fixation is likely to result in the improvement of existing nitrogen-fixing symbiotic or associative systems. Longer-term efforts are aimed at extending the nitrogen-fixing capacity to other organisms, including transfer of the genetic information for efficient nitrogen fixation into the plant genome and using current knowledge of microbe-plant interactions to extend symbiosis to cereals and, in particular, to rice. Related challenges in sustainable agriculture and forestry include the creation of new nitrogen-fixing associations. All of these approaches were discussed at the 11th International Congress on Nitrogen Fixation, Paris, France, July 20-25, 1997 and covered in the present proceedings volume.

In retrospect, it was obvious that we were both, quite inde pendently, contemplating a conference on the role of molybdenum in biology and related chemistry. At the time though, the meeting of minds on this matter was quite surprising. Although this subject has been treated in previous meetings within the overall context of, say, magnetic resonance or nitrogen fixation, it was apparent to us both that research in molybdenum-containing enzymes and molyb denum chemistry had progressed rapidly in the last several years. Jointly, we decided to organize the first meeting on Molybdenum Chemistry of Biological Significance which was held at the Hotel Lake Biwa, Shiga, Japan, on April 10-13, 1979. This volume con stitutes the Proceedings of that international conference and covers the broad spectrum of interests from enzymes to coordination chemistry. It should serve not only as a source of new information on the latest research results in this area and as a useful ref erence tool, but should also allow a newcomer or other peripherally interested researcher to become conversant very rapidly with the "state-of-the-art" in this specialized and important area of research. The conference was sponsored by the Japan Society for the Promotion of Science, the Japan World Exposition Commemerative Fund the Yamada Science Foundation, the Nissan Science Foundation, the Chemical Society of Japan (Kinki Regional Office) and the Agri cultural Chemical Society of Japan (Kansai Branch). We thank these organizations sincerely for their interest and generosity."

As for the preceding four International Symposia on Nitrogen Fixation, held in Pullman, Washington USA (1974); Salamanca, Spain (1976); Madison, Wisconsin, USA (1978); and Canberra, Australia (1980), the 5th Symposium held from August 28 - September 3, 1983 in Noordwijkerhout, The Netherlands, received the gene rous support of the Charles F. Kettering Foundation Research Laboratory and the Tennessee Valley Authority. This support has helped research progress in this broad field of science by offering a forum both for the exchange of ideas and for scientific summary and discussion as captured over the last 10 years in each of the four books published previously. Although all previous meetings were well attended, the present conference was the largest so far. 550 scien tists from 60 different countries attended the "Leeuwenhorst Conference", re presenting the many different disciplines actively involved in research in this field: chemists, biochemists, molecular biologists, geneticists, microbiologists, plant physiologists, agriculturalists. A large number of them had to go through a difficult period to raise the necessary funds to attend. In addition, a parallel meeting of "policymakers" from Southeast Asia, Africa and South America was held under the auspices of Crosscurrents International Institute, Dayton, OR, USA and the United Nations University, Tokyo, Japan. These participants attended some of the scientific sessions to benefit from the vision of a number of scientists at the symposium.

This Symposium, held August 4-10, 1985 on the campus of Oregon State University in Corvallis, is the sixth of a series of international symposia concerned with broad aspects of the fixation of nitrogen gas by biological and chemical means. The first symposium of this series was held in Pullman, Washington (1974), the second in Salamanca, Spain (1976), the third in Madison, Wisconsin (1978), the fourth in Canberra, Australia (1980) and the fifth in Noordwij erhout, The Netherlands (1983). Prior to the organization of these symposia, small groups of usually no more than 10 or 12 of the now "old guard" in the field met in some obscure places, including Butternut Lake, Wisconsin, Sanabel Island, Florida and Camp Sage hen in California, to discuss developments in the field. Concern about an energy crisis in the nineteen seventies served as an impetus for the organization of workshops and preparatiol. of publications urging government agencies to provide funds for the support of several neglected areas in the field, including the genetics of nitrogen-fixing organisms and the biology of Frankia. In looking back, it becomes apparent that there have been drastic changes in the extent of research support in the field and in the contents of the programs of the continuing series of symposia.

Biological nitrogen fixation provides more than 50% of the total annual input of the essential element nitrogen to world agriculture. Thus, it is of immense agronomic importance and critical to food supplies, particularly in developing countries.

This book, with chapters authored by internationally renowned experts, provides a comprehensive and detailed account of the fascinating history of the process - including the surprising discoveries of molybdenum-independent nitrogenases and superoxide-dependent nitrogenase; a review of Man's attempts to emulate the biological process - most successfully with the commercially dominant Haber-Bosch process; and the current state of the understanding art with respect to the enzymes - called nitrogenases - responsible for biological nitrogen fixation.

The initial chapters use a historical approach to the biological and industrial processes, followed by an overview of assay methodologies. The next set of chapters focuses on the classical enzyme, the molybdenum nitrogenase, and details its biosynthesis, structure, composition, and mechanism of action as well as detailing both how variants of its two component proteins are constructed by recombinant DNA technology and how computational techniques are being applied. The sophisticated chemical modelling of the metal-containing clusters in the enzyme is reviewed next, followed by a description of the two molybdenum-independent nitrogenases - first, the vanadium-containing enzyme and then the iron-only nitrogenase - together with some thoughts as to why they exist Then follows an up-to-date treatment of the clearly "non-classical" properties of the superoxide-dependent nitrogenase, which more closely resembles molybdenum-containing hydroxylases and related enzymes, like nitrate reductase, that it does the other nitrogenases. Each chapter contains an extensive list of references.

This book is the self-contained first volume of a comprehensive seven-volume series. No other available work provides the up-to-date and in-depth coverage of this series and this volume. This book is intended to serve as an indispensable reference work for all scientists working in this area, including agriculture and the closely related metals-in-biology area; to assist students to enter this challenging area of research; and to provide science administrators easy access to vital relevant information.

Poverty is a severe problem in Africa, Asia, South America and even in pockets of the developed world. Addressing poverty alleviation via the expanded use of biological nitrogen fixation in agriculture was the theme of the 15th International Congress on Nitrogen Fixation. Because nitrogen-fixation research is multidisciplinary, exploiting its benefits for agriculture and environmental protection has continued to attract research by diverse groups of scientists, including chemists, biochemists, plant physiologists, evolutionary biologists, ecologists, agricultural scientists, extension agents, and inoculant producers. The 15th International Congress on Nitrogen Fixation was held jointly with the 12th International Conference of the African Association for Biological Nitrogen Fixation. This joint Congress was hosted in South Africa at the Cape Town International Conv- tion Centre, 21-26 January 2007, and was attended by about 200 registered participants from 41 countries world-wide. During the Congress, some 100 oral and approximately 80 poster papers were presented. The wide range of topics covered and the theme of the Congress justifies this book's title, Nitrogen Fixation: Applications to Poverty Alleviation.

This book is the stand-alone final volume of a comprehensive series covering the basic and applied science relating to nitrogen fixation. It addresses the most important nitrogen-fixing symbiosis of all that between legumes and their root-nodule bacteria and therefore deals with the properties and behaviour of both macro- and micro-symbiont. The coverage is comprehensive, beginning with the extent of the symbiosis and how it may have arisen in the geological past. It considers how legumes select the root-nodule bacteria they allow to form nodules on their roots and the intricate series of signals to be exchanged between legume and bacteria for infection to occur. The immense progress in understanding the genetic systems in the bacteria necessary for nodulation is now being replicated in a rapidly increasing understanding of the required systems in the legumes. The cell biology of the processes of both infection and nodule development is analysed and leads to a parallel assessment of the biochemical processes in carbon and nitrogen metabolism required for successful nitroogen fixation by the symbiotic bacteroid. Attention is given to the ways in which the nodule has solved the conundrum of providing enough O2 for energy generation to drive nitrogen fixation without either inactivating the O2-sensitive nitrogenase or creating damaging reactive oxygen species. The volume also covers the basic physiology of the variety of root-nodule bacteria infecting legumes, as well as looking at the renewed controversy about the chemical form(s) of nitrogen exported to the legume. Successful exploitation of the legume symbiosis in agriculture, horticulture, and forestry demands an understanding of the ecology of the root-nodule bacteria particularly what makes for a successful inoculant strain for legume introduction to agricultural systems. Then, there is a requirement for inoculation technology to both successfully deliver viable bacteria to the root surface and facilitate nodulation. These practical aspects are thoroughly covered in the volume, with a final chapter assessing how the massive amount of recent information can be exploited in matching host and microsymbiont for the wide variety of environments in which they are needed in our production systems."

For researchers and graduates with any interest in plant or soil sciences, this fascinating study will be a godsend it s the complete state of the art with regard to actinorhizal symbioses. The self-contained sixth volume of a comprehensive series on nitrogen fixation, it includes chapters that deal with all aspects of this symbiosis between actinorhizal plants and nitrogen-fixing bacteria. It also contains information both about symbionts and their ecological role and use. Other chapters tackle the global distribution of different actinorhizal plants and their microsymbionts and how this impacts the question of co-evolution of the micro- and macrosymbionts as well as comparing the actinorhizal and leguminous symbioses. No other book provides the up-to-date and in-depth coverage of this volume."

Genetics and Regulation of Nitrogen-Fixing Bacteria This book is the second volume of a seven-volume series, which covers all fields of research related to nitrogen fixation - from basic studies through applied aspects to environmental impacts. Volume II provides a comprehensive and detailed source of information concerning the genetics and regulation of biological nitrogen fixation in free-living prokaryotes. This preface attempts to provide the reader with some insight into how this volume originated, how it was planned, and then how it developed over the several years of its production. Once the editorial team was established, the first job was to decide which of the many free-living diazotrophs that have been subjected to genetic analysis should be included in this volume. Would we need to develop specific criteria for selection or would the organisms, in effect, select themselves? Of course, Klebsiella pneumoniae and Azotobacter vinelandii, which have served (and still serve) as the main model organisms for the genetic analysis of diazotrophy, plus some of the other bacteria described in this volume, did indeed select themselves. However, there was considerable discussion surrounding well-characterized fixing species, like Azorhizobium caulinodans and Herbaspirillum seropedicae, both of which are able to fix atmospheric N under free-living conditions.

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.

In order to understand a process as complex as nitrogen fixation and to be in a position to manipulate it for the benefit of mankind, researchers are now working at the frontiers of science in many different areas: protein structure and function; catalytic mechanisms; electron transfer processes; regulatory circuits and environmental sensing; metabolic integration; chemical communication between organisms; differentiation; genome structure and function; microbial ecology; plant physiology; plant molecular biology; and agronomy. This volume represents a testimony to the advances in nitrogen fixation research that have been made and the contribution of these efforts to the solution of many other varied scientific problems. Limiting steps for future advances are analyzed and new horizons in nitrogen fixation research are proposed.

Genomes and Genomics of Nitrogen-fixing Organisms This is Volume 3 of a seven-volume series on all aspects of Nitrogen Fixation. The series aims to be the definitive authority in the field and to act as a benchmark for some years to come. Rather than attempting to cram the whole field into a single volume, the subject matter is divided among seven volumes to allow authors the luxury of writing in depth with a comprehensive reference base. All authors are recognized practicing scientists in the area of their contribution, which ensures the high quality, relevance, and readability of the chapters. In establishing the rationale for, and the organization of, this book, we realized the need to divide it into two sections. The first section should be organism based and should review our current knowledge of the genomes of nitrogen-fixing organisms and what these nucleotide sequences tell us. The second section should then be technology based. It should review what technologies are available to mine the data inherent in the nucleotide sequences and how they are now being used to produce gene-function data from differential gene expression.

This book is the self-contained fourth volume of a seven-volume comprehensive series on nitrogen fixation. The outstanding aspect of this book is the integration of basic and applied work on biological nitrogen fixation in the fields of agriculture, forestry, and ecology in general. Nowadays, the concept of sustainability, which originated in agriculture and land use, is reaching many other areas of society and industry. Sustainability has a major part to play in the global challenge of continued development of regions, countries, and continents all around the World and biological nitrogen fixation has a key role in this process. This volume begins with chapters specifically addressing crops of major global importance, such as soybeans, rice, and sugar cane. It continues with a second important focus, agroforestry, and describes the use and promise of both legume trees with their rhizobial symbionts and other nitrogen-fixing trees with their actinorhizal colonization. An over-arching theme of all chapters is the interaction of the plants and trees with microbes and this theme allows other aspects of soil microbiology, such as interactions with arbuscular mycorrhizal fungi and the impact of soil-stress factors on biological nitrogen fixation, to be addressed. Furthermore, a link to basic science occurs through the inclusion of chapters describing the biogeochemically important nitrogen cycle and its key relationships among nitrogen fixation, nitrification, and denitrification. The volume then provides an up-to-date view of the production of microbial inocula, especially those for legume crops. No other available work provides the up-to-date and in-depth coverage of this volume, which is intended to serve as an indispensable reference work for academic, government, and industrial scientists working in the applied areas of agronomy, plant breeding, plant nutrition, ecology, and forestry as well as those in the basic science areas of plant physiology, soil microbiology, and related environmental disciplines. This volume will be an invaluable tool for students entering this challenging area of research and will provide science administrators with ready access to vital relevant information.

This volume covers recent developments in both fundamental and applied research in biological nitrogen fixation. It emphasizes the application of biological nitrogen fixation for sustainable agriculture, which should lead to poverty alleviation, environmental protection, and good agricultural practices generally. The roles of, and advances in, plant breeding, plant molecular biology, nodule physiology, and symbiotic and associative interactions between plants and microbes in sustaining agricultural productivity and soil fertility are described. The evolution of symbioses and nitrogen fixation are also covered in this volume. To ensure high agricultural productivity, while protecting the environment (both soil and water resources), requires plant cultivars that also respond to beneficial microbes. The volume, therefore, describes the physiology and genomics of nitrogen-fixing bacteria together with the biochemistry and molecular genetics of the nitrogenase enzyme that actually fixes atmospheric nitrogen to a usable form.

This volume, which covers the most recent data on the role of nitrogen fixation in agriculture and forestry and on the biology of both plants and nitrogen-fixing microbes, is intended to serve as a useful reference for students and researchers, both in the laboratory (academic and commercial) and in the field.

Nodules produced on legume roots by root-nodule bacteria provide the major nitrogenous input into natural and agricultural systems worldwide. This book provides an in-depth and up-to-the-minute analysis of what is known about this symbiosis, its origins, the process of nodule formation and development, and the biochemistry and genetics of nodular nitrogen fixation. It also reviews the physiology of the root-nodule bacteria themselves, their ecology in both natural and agricultural systems, and how we can introduce new legumes along with the bacteria they require. This book is recommended for scientists working with root nodule bacteria or host legumes, agronomists, forestry scientists, and soil scientists.

This book is the self-contained sixth volume of a comprehensive series on nitrogen fixation. It presents the state-of-the-art in regards to actinorhizal symbioses. Like legumes, actinorhizal plants form root nodules that host nitrogen-fixing soil bacteria. However, because the macrosymbionts are, with one exception, woody plants rather than crop plants, actinorhizal symbioses are less well-known than legume symbioses to which they are phylogenetically related. Actinorhizal plants come from eight different families. They can grow on marginal soils by virtue of these symbioses and are used extensively in reforestation, soil reclamation, and desert agroforestry. The diversity of the involved host plants poses a variety of challenges to the actinorhizal symbiosis and results in interesting strategies, for example, to cope with the O2 dilemma or nutrient exchange between plant and bacterium. The actinorhizal micro-symbionts are Gram-positive actinomycetes of the genus Frankia...

This book is the self-contained fifth volume of a comprehensive seven-volume series covering both fundamental and applied aspects of nitrogen-fixation research since the 19th century. It addresses the issues arising from bacterial colonization of either the plant-root surface or other tissues as well as their modes of doing so. These associations are less formalized than the rhizobia-legume symbiosis but, as more and more of them are discovered, their myriad of effects on their plant hosts is becoming understood. Among the effects, in addition to often providing fixed nitrogen, plant growth can be promoted and plant diseases controlled. An understanding at the molecular level of the mechanisms by which these bacteria benefit crop productivity is an important issue in agriculture. This book describes the milestones in the discovery of the associative and endophytic nitrogen-fixing bacteria found intimately involved with cereal crops, forage grasses, and sugar cane.

This book is the self-contained fourth volume of a seven-volume comprehensive series on nitrogen fixation. The outstanding aspect of this book is the integration of basic and applied work on biological nitrogen fixation in the fields of agriculture, forestry, and ecology in general. Nowadays, the concept of sustainability, which originated in agriculture and land use, is reaching many other areas of society and industry. Sustainability has a major part to play in the global challenge of continued development of regions, countries, and continents all around the World and biological nitrogen fixation has a key role in this process. This volume begins with chapters specifically addressing crops of major global importance, such as soybeans, rice, and sugar cane. It continues with a second important focus, agroforestry, and describes the use and promise of both legume trees with their rhizobial symbionts and other nitrogen-fixing trees with their actinorhizal colonization. An over-arching theme of all chapters is the interaction of the plants and trees with microbes and this theme allows other aspects of soil microbiology, such as interactions with arbuscular mycorrhizal fungi and the impact of soil-stress factors on biological nitrogen fixation, to be addressed. Furthermore, a link to basic science occurs through the inclusion of chapters describing the biogeochemically important nitrogen cycle and its key relationships among nitrogen fixation, nitrification, and denitrification. The volume then provides an up-to-date view of the production of microbial inocula, especially those for legume crops. No other available work provides the up-to-date and in-depth coverage of this volume, whichis intended to serve as an indispensable reference work for academic, government, and industrial scientists working in the applied areas of agronomy, plant breeding, plant nutrition, ecology, and forestry as well as those in the basic science areas of plant physiology, soil microbiology, and related environmental disciplines. This volume will be an invaluable tool for students entering this challenging area of research and will provide science administrators with ready access to vital relevant information.

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.

This book is the self-contained third volume of a comprehensive series on nitrogen fixation. It presents the state-of-the-art in regards to genomic sciences applied to nitrogen-fixation research. The advent of genomic sciences represents a new era for biology. The classic paradigm based on the gene has now changed to a paradigm that is based on the genome. The knowledge of the complete nucleotide sequence of a genome and its consequences with regard to both transcription and translation lead to an integral and comprehensive view of the biochemistry and physiology of an organism. Moreover, comparative genomic studies provide new insights for a better understanding of the evolutionary process. Nitrogen-fixation research has fully entered the genomics era since the first complete nucleotide sequences of a rhizobial symbiotic plasmid and a methanogenic archaeon were first reported in 1997. Now, the complete nucleotide sequences of many genomes of nitrogen-fixing organism from different taxonomic groups are available. This volume includes chapters devoted to the genomes of specific organisms as well as chapters that cross organismal lines and analyse general aspects centred on functional genomics, genome dynamics, taxonomy, and evolution. No other available work provides the up-to-date and in-depth coverage of this volume, which is intended to serve as an indispensable reference work for academic, governmental, and industrial scientists working in the areas of genomics, transcriptomics, and proteomics, including those studying evolution and taxonomy; to assist students to enter this challenging area of research; and to provide science administrators with ready access to vital relevantinformation.

Biological nitrogen fixation provides more than 50% of the total annual input of the essential element nitrogen to world agriculture. Thus, it is of immense agronomic importance and critical to food supplies, particularly in developing countries.

This book, with chapters authored by internationally renowned experts, provides a comprehensive and detailed account of the fascinating history of the process - including the surprising discoveries of molybdenum-independent nitrogenases and superoxide-dependent nitrogenase; a review of Man's attempts to emulate the biological process - most successfully with the commercially dominant Haber-Bosch process; and the current state of the understanding art with respect to the enzymes - called nitrogenases - responsible for biological nitrogen fixation.

The initial chapters use a historical approach to the biological and industrial processes, followed by an overview of assay methodologies. The next set of chapters focuses on the classical enzyme, the molybdenum nitrogenase, and details its biosynthesis, structure, composition, and mechanism of action as well as detailing both how variants of its two component proteins are constructed by recombinant DNA technology and how computational techniques are being applied. The sophisticated chemical modelling of the metal-containing clusters in the enzyme is reviewed next, followed by a description of the two molybdenum-independent nitrogenases - first, the vanadium-containing enzyme and then the iron-only nitrogenase - together with some thoughts as to why they exist Then follows an up-to-date treatment of the clearly "non-classical" properties of the superoxide-dependent nitrogenase, which more closely resembles molybdenum-containing hydroxylases and related enzymes, like nitrate reductase, that it does the other nitrogenases. Each chapter contains an extensive list of references.

This book is the self-contained first volume of a comprehensive seven-volume series. No other available work provides the up-to-date and in-depth coverage of this series and this volume. This book is intended to serve as an indispensable reference work for all scientists working in this area, including agriculture and the closely related metals-in-biology area; to assist students to enter this challenging area of research; and to provide science administrators easy access to vital relevant information.

This book provides a comprehensive and detailed source of information on the genetic and regulatory aspects of biological nitrogen fixation in free-living (non-symbiotic) prokaryotes. Biological nitrogen fixation is represented in a diverse range of microorganisms, among which Klebsiella pneumoniae serves as a paradigm for the genetic analysis of diazotrophy, which is the ability to grow with N2 as sole nitrogen source. The volume uses two major complementary approaches to the subject matter. The initial chapters use an organismic-based approach by concentrating on the well-characterized diazotrophic proteobacteria, cyanobacteria, Gram-positive clostridia, and Archea. The later chapters use a comparative process-based approach and serve as overviews dealing with different regulatory aspects, electron transport to nitrogenase, and molybdenum metabolism, across the range of organisms. Whenever appropriate, historical aspects and agricultural and ecological impacts have been taken into consideration. Each chapter contains an extensive list of references. This book is the self-contained second volume of a comprehensive seven-volume series. No other available work provides the up-to-date and in-depth coverage of this series and this volume. This book is intended to serve as an indispensable reference work for all scientists working in this and closely related fields, to assist students to enter this challenging area of research, and to provide science administrators easy access to vital relevant information.

These proceedings bring together diverse disciplines that study nitrogen fixation and describe the most recent advances made in various fields: chemists are now studying FeMoco, the active site of nitrogenase in non-protein surroundings, and have refined the crystal structure of the enzyme to 1.6 angstroms.

The refinement of molecular techniques and the development of new probes of the phylogeny of diazotrophs has revealed an extreme biodiversity among the nitrogen fixers, which helps explain the role that nitrogen fixation plays in maintaining life on Earth. The most efficient ecosystems are those where the bacteria are associated with a plant in differentiated organs to benefit crop productivity. Most short-term benefit from fundamental research on nitrogen fixation is likely to result in the improvement of existing nitrogen-fixing symbiotic or associative systems. Longer-term efforts are aimed at extending the nitrogen-fixing capacity to other organisms, including transfer of the genetic information for efficient nitrogen fixation into the plant genome and using current knowledge of microbe-plant interactions to extend symbiosis to cereals and, in particular, to rice. Related challenges in sustainable agriculture and forestry include the creation of new nitrogen-fixing associations. All of these approaches were discussed at the 11th International Congress on Nitrogen Fixation, Paris, France, July 20-25, 1997 and covered in the present proceedings volume.