nitrogenfixing

Nitrogen fixing is the process by which inert atmospheric nitrogen (N2) is converted into biologically usable forms, such as ammonia (NH3) or related nitrogen compounds. Most fixed nitrogen enters ecosystems through biological and industrial pathways rather than direct atmospheric uptake.

Biological nitrogen fixation is carried out mainly by certain prokaryotes that possess the enzyme nitrogenase, which reduces N2 to ammonia. This reaction requires substantial energy in the form of ATP and is highly sensitive to oxygen. In nature, nitrogen fixation occurs in several contexts: free-living soil and aquatic bacteria (for example, Azotobacter and some cyanobacteria), symbiotic bacteria in root nodules of legumes (Rhizobium, Bradyrhizobium, Sinorhizobium), and actinorhizal plants (Frankia), as well as cyanobacteria that form specialized cells called heterocysts. Plants assimilate the resulting ammonia or ammonium into amino acids through established metabolic pathways.

Industrial nitrogen fixation, most prominently the Haber-Bosch process, converts N2 and hydrogen into ammonia under high temperature and pressure with an iron catalyst. This ammonia is a cornerstone of synthetic fertilizers and has profoundly influenced modern agriculture, economy, and global nitrogen cycles.

Ecological and agricultural significance stems from nitrogen fixation as a primary source of reactive nitrogen, which supports plant growth and soil fertility. Management strategies to optimize fixation and minimize environmental impact include crop rotation with legumes, inoculation with effective nitrogen-fixing strains, and breeding or engineering crops to utilize fixed nitrogen more efficiently.