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The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes.
In 2002 however, anammox was found to play an important part in the biological nitrogen cycle, accounting for 24–67% of the total N 2 production in the continental shelf sediments that were studied. [31] [32] The discovery of anammox process modified the concept of biological nitrogen cycle, as depicted in Figure 2.
The oceanic nitrogen cycle with the role of DNRA. Blue line represents the ocean surface, with the atmosphere above. Notice how NH 4 produced by DNRA can be taken up by biota and converted into organic nitrogen, while N 2 produced by denitrification is removed from the system, and may only re-enter via nitrogen fixation.
A biogeochemical cycle, or more generally a cycle of matter, [1] is the movement and transformation of chemical elements and compounds between living organisms, the atmosphere, and the Earth's crust. Major biogeochemical cycles include the carbon cycle, the nitrogen cycle and the water cycle. In each cycle, the chemical element or molecule is ...
Nitrogen is a chemical element; ... The nitrogen cycle describes the movement of the element from the air, ... (see figure at right), ...
Figure 1: The nitrogen cycle in a soil-plant system. One potential pathway: N is fixed by microbes into organic compounds, which are mineralized (i.e. ammonification) and then oxidized to inorganic forms (i.e. nitrification) that are assimilated by plants (NO 3 −).
Nitrogen is a critical chemical element in both proteins and nucleic acids, and thus every living organism must metabolize nitrogen to survive. Only bacteria and Archaea are able to convert nitrogen gas (N 2 ) to and from soluble ionic compounds that other organisms can metabolize.
Nitrogen enters the ocean through precipitation, runoff, or as N 2 from the atmosphere. Nitrogen cannot be utilized by phytoplankton as N 2 so it must undergo nitrogen fixation which is performed predominantly by cyanobacteria. [82] Without supplies of fixed nitrogen entering the marine cycle, the fixed nitrogen would be used up in about 2000 ...