Editing Cyanobacteria (section)

== Nitrogen fixation ==
[[File:Nitrogen-fixing cyanobacteria.png|thumb|{{center|Nitrogen-fixing cyanobacteria}}]]

Some cyanobacteria can fix atmospheric [[nitrogen]] in anaerobic conditions by means of specialized cells called [[heterocyst]]s.<ref name="Golden_1998" /><ref name="Fay_1992" /> Heterocysts may also form under the appropriate environmental conditions (anoxic) when fixed nitrogen is scarce. Heterocyst-forming species are specialized for nitrogen fixation and are able to fix nitrogen gas into [[ammonia]] ({{chem2|NH3}}), [[nitrites]] ({{chem2|NO2-}}) or [[nitrates]] ({{chem2|NO3-}}), which can be absorbed by plants and converted to protein and nucleic acids (atmospheric nitrogen is not [[bioavailable]] to plants, except for those having endosymbiotic [[nitrogen-fixing bacteria]], especially the family [[Fabaceae]], among
others). Nitrogen fixation commonly occurs on a cycle of nitrogen fixation during the night because photosynthesis can inhibit nitrogen fixation.<ref>{{Cite journal |last1=Berman-Frank |first1=Ilana |last2=Quigg |first2=Antonietta |last3=Finkel |first3=Zoe V. |last4=Irwin |first4=Andrew J. |last5=Haramaty |first5=Liti |date=2007 |title=Nitrogen-fixation strategies and Fe requirements in cyanobacteria |journal=Limnology and Oceanography |language=en |volume=52 |issue=5 |pages=2260–2269 |doi=10.4319/lo.2007.52.5.2260 |bibcode=2007LimOc..52.2260B }}</ref>

Free-living cyanobacteria are present in the water of [[paddy field|rice paddies]], and cyanobacteria can be found growing as [[epiphyte]]s on the surfaces of the green alga, ''[[Chara (alga)|Chara]]'', where they may fix nitrogen.<ref>
{{cite journal |vauthors=Sims GK, Dunigan EP |year=1984 |title=Diurnal and seasonal variations in nitrogenase activity {{chem|C|2|H|2}} reduction) of rice roots |journal=Soil Biology and Biochemistry |volume=16 |issue=1 |pages=15–18 |doi=10.1016/0038-0717(84)90118-4}}</ref> Cyanobacteria such as ''[[Anabaena]]'' (a symbiont of the aquatic fern ''[[Azolla]]'') can provide rice plantations with [[biofertilizer]].<ref name="Azolla-Anabaena as a Biofertilizer for Rice Paddy Fields in the Po Valley, a Temperate Rice Area in Northern Italy">{{cite journal |title=Azolla-Anabaena as a Biofertilizer for Rice Paddy Fields in the Po Valley, a Temperate Rice Area in Northern Italy |journal=[[International Journal of Agronomy]] |doi=10.1155/2010/152158 |year=2010 | vauthors = Bocchi S, Malgioglio A |volume=2010 |pages=1–5 |doi-access=free|hdl=2434/149583 |hdl-access=free }}</ref>

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