Establishing symbiotic nitrogen fixation in cereals and other non-legume crops: The Greener Nitrogen Revolution
Haber’s invention of the synthesis of ammonia from its elements is one of the cornerstones of modern civilization. For nearly a century, agriculture has come to rely on synthetic nitrogen fertilizers produced from ammonia. This large-scale production is now supporting nearly half of the world’s population through increased food production. But whilst the use of synthetic nitrogen fertilizers brought enormous benefits, including those of the Green Revolution, the world needs to disengage from our ever-increasing reliance on nitrogen fertilizers produced from fossil fuels. Their pollution of the atmosphere and water systems has become a major global environmental and economic concern. Naturally, legume crops such as peas and beans can fix nitrogen symbiotically by interacting with soil nitrogen-fixing rhizobia, bacteria that become established intracellularly within root nodules. Ever since this was first demonstrated in 1888, consistent attempts have been made to extend the symbiotic interaction of legumes with nitrogen-fixing bacteria to non-legume crops, particularly cereals. In 1988, a fresh impetus arose from the discovery of Gluconacetobacter diazotrophicus (Gd), a non-nodulating, non-rhizobial, nitrogen-fixing bacterium isolated from the intercellular juice of sugarcane. Subsequently, strains of Gd inoculated under specific conditions were shown to intracellularly colonize the roots and shoots of the cereals: wheat, maize (corn) and rice, as well as crops as diverse as potato, tea, oilseed rape, grass and tomato. An extensive field trials programme using a seed inoculum technology based on Gd (NFix®) indicates that NFix® is able to significantly improve yields of wheat, maize, oilseed rape and grasses, in both the presence and absence of synthetic nitrogen fertilizers. Evidence suggests that these benefits are accruing through a possible combination of intracellular symbiotic nitrogen fixation, enhanced rates of photosynthesis and the presence of additional plant growth factors. Here, we discuss the research events that have led to this important development and present results demonstrating the efficacy of NFix® technology in non-legume crops, in particular cereals.