Nitrogen fixation
Nitrogen fixation is the process by which
nitrogen is taken from its relatively inert molecular form in the
atmosphere and converted into nitrogen compounds useful for other chemical processes .
Nitrogen fixation is performed naturally by a number of different prokaryotes, including
bacteria, and actinobacteria certain types of anaerobic bacteria. Microorganisms that fix nitrogen are called diazotrophs. Some higher plants, and some animals , have formed associations with diazotrophs.
Biological nitrogen fixation was discovered by the Dutch microbiologist Martinus Beijerinck.
Encyclopedia
Nitrogen fixation is the process by which
nitrogen is taken from its relatively inert molecular form in the
atmosphere and converted into nitrogen compounds useful for other chemical processes .
Nitrogen fixation is performed naturally by a number of different prokaryotes, including
bacteria, and actinobacteria certain types of anaerobic bacteria. Microorganisms that fix nitrogen are called diazotrophs. Some higher plants, and some animals , have formed associations with diazotrophs.
Biological nitrogen fixation was discovered by the Dutch microbiologist Martinus Beijerinck.
Biological Nitrogen Fixation
Biological Nitrogen Fixation occurs when atmospheric nitrogen is converted to ammonia by a pair of bacterial enzymes called nitrogenase . The formula for BNF is:
- N2 + 8H+ + 8e- + 16 ATP ? 2NH3 + H2 + 16ADP + 16 Pi
Although
ammonia is the direct product of this reaction, it is quickly ionized to
ammonium . In free-living diazotrophs, the nitrogenase-generated ammonium is assimilated into
glutamate through the glutamine synthetase/glutamate synthase pathway.
In most bacteria, the nitrogenase enzymes are very susceptible to destruction by oxygen . Low oxygen tension is achieved by different bacteria by: living in anaerobic conditions, respiring to draw down oxygen levels, or binding the oxygen with a protein .
Leguminous nitrogen-fixing plants
The best-known are
legumes which contain
symbiotic bacteria called
rhizobia within
nodules in their
root systems, producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the nitrogen helps to fertilize the
soil . The great majority of legumes have this association, but a few genera do not.
Non-leguminous nitrogen fixing plants
Plants from many other families have similar associations, including:
Chemical nitrogen fixation
Nitrogen can also be artificially fixed for use in
fertilizer, explosives, or in other products. The most popular method is by the Haber process. Artificial fertilizer production has achieved such scale that it is now the largest source of fixed nitrogen in the
Earth's ecosystem.
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