Understanding and Exploiting Biological Nitrogen Fixation for Improvement of Brazilian Agriculture

After water, available nitrogen is the most limiting nutrient for plant growth. Although the demand for fixed nitrogen can be met by the use of chemical fertilisers, their use in agriculture has resulted in major environmental and economic impacts. At present less than half of the nitrogen used by farmers is assimilated by crops. Excess nitrogen leaks into the environment, leading to significant effects on soil and water quality, biodiversity, and atmospheric pollution. However, some bacteria can perform a process known as biological nitrogen fixation, which converts nitrogen gas from the atmosphere into ammonia, a source of nitrogen that can be assimilated by animals and plants. This provides a more sustainable alternative to the use of synthetic fertilisers.

Although soil-dwelling nitrogen fixing bacteria can associate with food and energy crops, they do not readily release their fixed nitrogen for the benefit of the plant, although they can have beneficial effects on plant growth. In Brazil, significant increases in crop yield have been observed in response to inoculation with nitrogen fixing bacteria, some of which have an endophytic lifestyle and can gain access to intercellular spaces in plant roots and shoots. This provides an opportunity to engineer closer associations between nitrogen-fixing bacteria and food and energy crops, in which fixed nitrogen is delivered more effectively to the plant. This proposal for a Virtual Joint Centre (VJC) brings together a team of Brazilian and UK investigators focused towards understanding and exploiting plant-diazotroph interactions as a means to enhance agricultural productivity in Brazil. Using fundamental knowledge of nitrogen regulation in endophytic nitrogen fixing bacteria, we will engineer strains, which excrete ammonium to benefit crop growth, and examine the potential of these modified strains as inoculants. We will also design selection strategies to isolate associative diazotrophs that are competitive in the rhizosphere in relation to plant varieties that respond well and have a growth advantage in the presence of these endophytes. We will identify genes required for efficient plant-microbe interactions and quantitate the level of biological, nitrogen fixation in relation to crop yield. Finally, we will we examine the potential for the use of native and engineered strains as inoculants. To achieve these objectives, we will exploit strong synergies and world-leading expertise of UK and Brazilian researchers in biological nitrogen fixation, microbial population dynamics, bacterial and plant genetics, genomics and synthetic biology, in order to engineer efficient cultivar-endophyte combinations and develop improved inoculant technologies. Enhancing nitrogen fixation in our target crops promises substantial benefits for Brazilian agriculture, while decreasing the use and environmental impact of industrial nitrogen fertilisers.

Application of chemical fertilisers has maintained high crop yields in many countries, but has resulted in severe perturbation of the global biogeochemical nitrogen cycle, resulting in greenhouse gas emissions and consequent acute damage to human health and ecosystem services. We are faced with the dilemma of reducing chemical nitrogen input into agriculture but at same time increasing yields to feed the growing world population and maintain global food security. Biological nitrogen fixation provides a more sustainable route to supply nitrogen to crops and as we propose here, can be exploited to enhance crop productivity while mitigating the consequences of reactive nitrogen release. This promises enormous benefit for humanity through the reduction of greenhouse gas emissions and development of sustainable agriculture. The impacts of this research will be global in the long term, benefiting not only academia, industry and the farming community, but also substantial socio-economic benefits on an international scale.

The academic sector will benefit in the short to medium term as the proposed research will provide publications, knowledge, expertise and materials of direct relevance to biological nitrogen fixation and agriculture on an international, multidisciplinary level.

We intend to communicate our research activities to a range of audiences including those in schools and cafe scientific environments to help raise the underlying issues and to illustrate biotechnological solutions to worldwide challenges to achieve a sustainable planet.

The farming community and the agro-industrial sector will benefit in the medium to long-term from the development of biofertiliser strains identified by the VJC, which will be validated in field trials and evaluated to control the quality and the development of new commercial inoculants, which will be disseminated to farmers and representatives of the biofertiliser industry in Brazil.

Tackling the nitrogen problem with sustainable biotechnological solutions such as those proposed here is likely to yield enormous economic, social and ecosystem impacts, through reduced costs of nitrogen inputs in agriculture together with the added benefit of decreased greenhouse gas emissions.