Opportunities For Biological Nitrogen Fixation In Rice And Other Non Legumes

Proceedings of the Second Working Group Meeting of the Frontier Project on Nitrogen Fixation in Rice held in Faisalabad, Pakistan, 13-15 October 1996

This text looks at the advances in understanding symbiotic Rhizobium-legume interactions at the molecular level, the discovery of endophytic interactions of nitrogen-fixing organisms with non-legumes and the ability to introduce new genes into rice through transformation. This has created an opportunity to investigate the possibilities for incorporating N2 fixation capability in rice. During a think-tank workshop organized by IRRI in 1992, the participants reaffirmed that such opportunities do exist for cereals and recommended that rice be used as a model system. Subsequently, IRRI developed a New Frontier Project to co-ordinate the worldwide collaborative efforts among research centers committed to reducing dependency of rice on mineral N resources. An international Rice Biological Nitrogen Fixation (BNF) working group was established to review, share research results/materials, and to catalyze research.

During the next 30 years, farmers must produce 70% more rice than the 550 millions tons produced today to feed the increasing population. Nitrogen (N) is the nutrient that most frequently limits rice production. At current levels ofN use efficiency, we will require at least double the 10 million tons of N fertilizer that are currently used each year for rice production. Global agriculture now relies heavily on N fertilizers derived from petroleum, which, in turn, is vulnerable to political and economic fluctuations in the oil markets. N fertilizers, therefore, are expensive inputs, costing agriculture more than US$45 billion annually. Rice suffers from a mismatch of its N demand and N supplied as fertilizer, resulting in a 50-70% loss of applied N fertilizer. Two basic approaches may be used to solve this problem One is to regulate the timing ofN application based on needs of the plants, thus partly increasing the efficiency of the plants' use of applied N. The other is to increase the ability of the rice system to fix its own N. The latter approach is a long-term strategy, but it would have enormous environmental benefits while helping resource-poor farmers. Furthermore, farmers more easily adopt a genotype or variety with useful traits than they do crop and soil management practices that may be associated with additional costs.

Nitrogen is arguably the most important nutrient required by plants. However, the availability of nitrogen is limited in many soils and although the earth's atmosphere consists of 78.1% nitrogen gas (N2) plants are unable to use this form of nitrogen. To compensate , modern agriculture has been highly reliant on industrial nitrogen fertilizers to achieve maximum crop productivity. However, a great deal of fossil fuel is required for the production and delivery of nitrogen fertilizer. Moreover carbon dioxide (CO2) which is released during fossil fuel combustion contributes to the greenhouse effect and run off of nitrate leads to eutrophication of the waterways. Biological nitrogen fixation is an alternative to nitrogen fertilizer. It is carried out by prokaryotes using an enzyme complex called nitrogenase and results in atmospheric N2 being reduced into a form of nitrogen diazotrophic organisms and plants are able to use (ammonia). It is this process and its major players which will be discussed in this book. Biological Nitrogen Fixation is a comprehensive two volume work bringing together both review and original research articles on key topics in nitrogen fixation. Chapters across both volumes emphasize molecular techniques and advanced biochemical analysis approaches applicable to various aspects of biological nitrogen fixation. Volume 1 explores the chemistry and biochemistry of nitrogenases, nif gene regulation, the taxonomy, evolution, and genomics of nitrogen fixing organisms, as well as their physiology and metabolism. Volume 2 covers the symbiotic interaction of nitrogen fixing organisms with their host plants, including nodulation and symbiotic nitrogen fixation, plant and microbial "omics", cyanobacteria, diazotrophs and non-legumes, field studies and inoculum preparation, as well as nitrogen fixation and cereals. Covering the full breadth of current nitrogen fixation research and expanding it towards future advances in the field, Biological Nitrogen Fixation will be a one-stop reference for microbial ecologists and environmental microbiologists as well as plant and agricultural researchers working on crop sustainability.

Diazotrophic bacteria convert atmospheric nitrogen to plant-useable form and this input of nitrogen through biological fixation is of great agronomic importance. The contributions presented in this volume relate to free-living nitrogen fixers and the diazotrophs associated with plants. Symbiotic association of Frankia with non-legumes and cyanobacterial associations are also discussed. Research topics covered in this volume include the biochemistry and genetics of diazotrophs, recent developments in improvement of plant-microbe interactions and their molecular basis, the use of molecular probes in taxonomy and ecology of diazotrophs and reports on field applications, agronomic importance and improvement in methodologies for assessing their contribution to plants. This book provides valuable information not only for researchers working in the field of biological nitrogen fixation but also for biochemistry, molecular biologists, microbiologists and agronomists.

This book covers aspects of biological nitrogen fixation along with the unique signaling and interaction between the diazotrophic bacteria and plants, especially the non-legumes. Nitrogen is the most important growth-limiting nutrient in the ecosystems and biological nitrogen fixation involving microbial symbionts, mainly rhizobia and legumes holds enormous interest across the globe. However, free-living rhizobacteria of non-legumes especially cereals, also establish themselves within the root system, fixing nitrogen and contributing to plant productivity, soil fertility, and agricultural sustainability. These non-symbiotic nitrogen fixers additionally exhibit various plant growth-promoting traits elevating productivity, fortifying nutrient content, and managing water stress in plants. The recent perspectives highlighting the mechanisms and background of non-symbiotic nitrogen fixation provide answers to unravel the potential of nitrogenase and various spectra of habitats of rhizobia and other diazotrophic bacteria. Further, the application of genetic engineering and the development of nitrogen-fixing cereals can provide a possible solution to the problem of food shortage. The book includes various scientific inputs providing comprehensive knowledge about the emergence of agricultural sustainability through nitrogen-fixing bacteria. The book illustrates the systematic mechanisms involved in biological nitrogen fixation through various illustrations, schematic drawings, and flow charts aiding in better understanding. The chapters elaborate on the physiology and metabolism of plant-bacteria interaction in different crops under diverse environmental conditions. Thus, the volume will provide a holistic scenario helping in advancing the novel plant-microbe interactions, cell-signaling, and plant-molecular interactions. The book will assist the agronomists, microbiologists, ecologists, plant pathologists, molecular biologists, environmentalists, policymakers, conservationists, and NGOs to develop biofertilizers and bioinoculants using various genera of microbes and contribute to the targets of sustainable goals in an eco-friendly manner.

This book features the latest research advances made in developing nitrogen-fixing rice.