Nitrogen Fixation

Plants and humans can only absorb and use ‘fixed’ nitrogen, thus producing fixed nitrogen that is an essential component of life

Nitrogen Fixation has been an area of research at the John Innes Centre for almost half a century.

Plants and humans can only absorb and use ‘fixed’ nitrogen. This is a form of nitrogen combined with hydrogen (to form ammonia) or oxygen (to form nitrate).

Nitrogen is abundant as a gas in the atmosphere, but gaseous nitrogen is unusable by plants and animals.

However, by carrying out the process of biological nitrogen fixation, bacteria and archaea can convert nitrogen gas to ammonia, thus producing fixed nitrogen that is an essential component of life, being a key element in many biomolecules, including for example DNA and proteins.

Some plants, such as legumes, create a symbiotic relationship with nitrogen-fixing bacteria called rhizobia that infect the plant, which in response to the bacteria develops structures known as nodules on the legume roots.

Within the root nodules the symbiotic bacteria develop into organelles that act like nitrogen fixing factories to supply nitrogen to the crop in exchange for carbon provided by the plant. The legume symbiosis is very efficient and can supply all the nitrogen demands of the crop. It is therefore a prototype for engineering nitrogen fixation in the future.

In addition to the legume symbiosis, nitrogen-fixing soil bacteria can associate with cereal crops to meet some of their nitrogen requirements. This process can be improved by inoculating cereals with nitrogen fixing bacteria as biofertilsers.

There are many biofertiliser companies throughout the world that prepare inoculant formulations and sell these to farmers. However, in general this technology is neither as efficient or robust as the legume symbiosis and year to year variations in yield are experienced by farmers. But inoculants are far cheaper than nitrogen fertilisers, so provide cost savings for farmers.

This technology is influenced by plant genotype, climate and soil type and appears to work better in some locations compared with others.