lämmastikuringlust

Lämmastikuringlust, also known as nitrogen fixation, is a biological process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related nitrogenous compounds. This essential process enables organisms to incorporate nitrogen into their biological molecules, such as amino acids and nucleic acids, which are fundamental to life.

The primary agents of nitrogen fixation are certain bacteria and archaea, some of which live freely in the soil or water, while others form symbiotic relationships with plants, particularly legumes. The most well-known example is the genus *Rhizobium*, which infects the root nodules of leguminous plants like peas, beans, and clover. This mutualistic partnership allows the plant to access fixed nitrogen, promoting growth, while the bacteria receive carbohydrates produced by photosynthesis.

Non-symbiotic nitrogen fixation also occurs through free-living bacteria such as *Azotobacter* and cyanobacteria (e.g., *Anabaena* and *Nostoc*), which thrive in aquatic and moist terrestrial environments. Additionally, certain industrial processes, such as the Haber-Bosch method, artificially fix nitrogen for agricultural use, producing ammonia from nitrogen gas and hydrogen.

Nitrogen fixation is critical for ecosystems, as it replenishes soil nitrogen levels, which are often depleted by plant uptake and microbial activity. Without this process, many organisms would lack access to usable nitrogen, limiting primary productivity and disrupting food chains. However, excessive nitrogen input—whether from natural or anthropogenic sources—can lead to environmental issues, such as eutrophication and increased greenhouse gas emissions.