lämmastikuringe

Lämmastikuringe, also known as the nitrogen cycle, is the biogeochemical process by which nitrogen is converted in various chemical forms as it circulates among the atmosphere, terrestrial ecosystems, and marine ecosystems. Nitrogen is an essential element for all living organisms, playing a vital role in the formation of amino acids, proteins, and nucleic acids. However, atmospheric nitrogen gas (N2) is largely unavailable to most organisms due to its stable triple bond.

The cycle begins with nitrogen fixation, where atmospheric N2 is converted into ammonia (NH3) or ammonium (NH4+). This process can be carried out by nitrogen-fixing bacteria, lightning, or industrial processes. Ammonia is then converted to nitrites (NO2-) and nitrates (NO3-) through nitrification, primarily by soil bacteria. Nitrates are the form of nitrogen most readily absorbed by plants.

Plants assimilate nitrates and incorporate them into their organic compounds. When animals consume plants or other animals, they obtain nitrogen. Decomposition, carried out by decomposers like bacteria and fungi, breaks down organic matter, releasing nitrogen back into the soil as ammonia. This process is called ammonification.

Finally, denitrification, performed by denitrifying bacteria, converts nitrates back into atmospheric nitrogen gas (N2), completing the cycle. This gaseous nitrogen is then released back into the atmosphere, where it can begin the cycle anew. Disruptions to the nitrogen cycle, such as through excessive use of fertilizers, can lead to environmental problems like eutrophication of water bodies.