nitrogénellátását

Nitrogénellátás, or nitrogen fixation, is a biological process by which atmospheric nitrogen (N2) is converted into ammonia (NH3) or other nitrogenous compounds, making it available for use by living organisms. This process is crucial for the nitrogen cycle, as it provides a source of nitrogen for plants, which cannot directly assimilate atmospheric nitrogen. Nitrogen fixation is primarily carried out by certain bacteria and archaea, known as diazotrophs, which have the enzyme nitrogenase. This enzyme catalyzes the reduction of N2 to NH3 under anaerobic conditions, using ATP and a reducing agent such as ferredoxin or flavodoxin.

There are two main types of nitrogen fixation: symbiotic and free-living. Symbiotic nitrogen fixation occurs in associations between diazotrophic bacteria and plant roots, such as in legumes (e.g., peas, beans, and clover) and non-legumes (e.g., alder and mycorrhizal fungi). Free-living nitrogen fixation occurs in soil and aquatic environments, where diazotrophic bacteria can fix nitrogen independently of plants. Examples of free-living diazotrophs include Azotobacter, Beijerinckia, and Clostridium.

Nitrogen fixation is an energy-intensive process, requiring up to 16 ATP molecules per N2 molecule fixed. This energy demand is a significant factor in the distribution and abundance of diazotrophs in various ecosystems. Additionally, nitrogen fixation can produce reactive oxygen species as a byproduct, which can be harmful to the cells if not properly managed.

The global annual nitrogen fixation rate is estimated to be around 100-200 teragrams of nitrogen per year, with about 50% of this amount fixed by symbiotic associations and the remaining 50% by free-living diazotrophs. Human activities, such as the use of nitrogen fertilizers and industrial nitrogen fixation, have significantly altered the global nitrogen cycle, leading to increased nitrogen availability and potential environmental impacts, including eutrophication and greenhouse gas emissions.