How does nitrogen fixation help plant growth

Fertilize grain with nitrogen-fixing bacteria

Nitrogen is considered to be the engine of plant growth. Farmers around the world rely on nitrate fertilizers to increase their yields. But there are plants like sugar cane that can do without the extremely energy-intensive fertilizers. The trick: With the help of bacteria that are stored in and on the roots, they bind nitrogen directly from the air and thus supply themselves. In the research project "NITRO-SUS", molecular biologists led by Barbara Reinhold-Hurek from the University of Bremen have been looking for things since 2011 genomic approaches to improve nitrogen sustainability in cereals. The team is experimenting with wild rice, which also has nitrogen-fixing bacteria. Their goal: to transfer the nitrogen fixation potential of the wild plant to the cultivated rice by means of genetic engineering or crossbreeding and thus to reduce the nitrogen fertilization of rice plants and other cereals in the long term. The research project is supported by the Federal Ministry of Education and Research (BMBF) with around 1 million euros.

Nitrogen is the fuel that stimulates plant growth and makes the soil fertile. Grain fields around the world are therefore sprinkled with artificial nitrogen fertilizers in order to sprout wheat or barley and to bring in a rich harvest. The reason: unlike legumes such as beans, peas or lupins, which bind nitrogen with the help of bacteria in the roots, grain cannot supply itself with this nutrient, although a sea of ‚Äč‚Äčnatural nitrogen is floating in the atmosphere. Because 78 percent of the air consists of nitrogen gas.

Encourage grain growth in a natural way

Barbara Reinhold-Hurek is committed to using this sustainable resource to naturally stimulate the growth of grain. The microbiologist and geneticist heads the BMBF-funded research project "NITRO-SUS" at the University of Bremen. Reinhold-Hurek and her team are looking for genetic approaches for nitrogen-sustainable and environmentally friendly grain production. Knowledge of plants, which naturally have nitrogen-fixing abilities, should help. "Artificial fertilizer is not only a cost factor, but also a burden on the environment. If nitrogen is supplied by bacteria, it is definitely more sustainable," explains Reinhold, who has been dealing with the subject for decades. The aim of the researchers involved in the "NITRO-SUS" project is to transfer this fixation potential to cultivated plants.

Research focuses on rice

In the laboratory, the Bremen researchers first examined numerous wild plants for their bacterial activity in the roots. "This is how we found the wild type of rice. Here, the bacterial activity in terms of nitrogen fixation seemed to be particularly high. In addition, this rice also grows very well on nutrient-poor soils." To transfer nitrogen fixation potential from wild rice to cultivated rice. They go two different ways. On the one hand, they try to select suitable genes from wild rice through which the plant can cooperate particularly well with bacteria for nitrogen supply. " We introduced a parallel approach in cultivated rice plants to see whether we can improve the process in these genetically modified plants, "explains the researcher. In parallel, the team is trying to achieve this effect by crossing wild rice with cultivated rice. These breeding experiments were carried out together with the International Rice Research Institute (IRR I) performed in the Philippines. While the genetic engineering experiment has not yet been fully completed, the first "promising" results are showing with conventional breeding, reports Reinhold-Hurek. "With some, the nitrogen fixation increased, so that something on the plant is likely to change through interaction."