nitrogénfixáció

Nitrogénfixáció refers to the biological or chemical process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related nitrogenous compounds, making it accessible for biological use. This process is essential for ecosystems as it provides a key nutrient for plant growth, which in turn supports the broader food chain.

The primary biological nitrogénfixáció occurs through certain bacteria and archaea, either freely living in the soil or in symbiotic relationships with plants. Leguminous plants, such as peas, beans, and clover, host rhizobia bacteria in their root nodules, where these microbes convert atmospheric nitrogen into ammonia. Non-legume plants can also associate with nitrogen-fixing bacteria, such as cyanobacteria (e.g., *Anabaena* and *Nostoc*), which form symbiotic relationships with certain ferns and cycads.

Non-symbiotic nitrogénfixáció occurs in the soil through free-living bacteria like *Azotobacter* and *Clostridium*, as well as in aquatic environments by cyanobacteria. These organisms possess the enzyme nitrogenase, which catalyzes the reduction of nitrogen gas (N₂) to ammonia (NH₃) under anaerobic or low-oxygen conditions. This process requires significant energy, often derived from organic compounds or photosynthesis.

Chemical nitrogénfixáció occurs naturally through lightning, which produces nitrates that are carried to the soil by rain. Industrially, the Haber-Bosch process synthesizes ammonia from nitrogen and hydrogen under high pressure and temperature, a method critical for modern agriculture.

Nitrogénfixáció is a fundamental ecological process, ensuring nitrogen availability for primary producers and maintaining soil fertility. However, excessive nitrogen input, whether from natural or anthropogenic sources, can lead to environmental issues such as eutrophication and disruption of nitrogen cycles.