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Nitrogen fixation is a chemical process by which molecular
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
(), with a strong triple covalent bond, in the
air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
is converted into
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
() or related nitrogenous compounds, typically in soil or aquatic systems but also
in industry IN, In or in may refer to: Places * India (country code IN) * Indiana, United States (postal code IN) * Ingolstadt, Germany (license plate code IN) * In, Russia, a town in the Jewish Autonomous Oblast Businesses and organizations * Indepen ...
. Atmospheric nitrogen is molecular dinitrogen, a relatively nonreactive molecule that is metabolically useless to all but a few microorganisms. Biological nitrogen fixation or ''diazotrophy'' is an important microbials mediated process that converts dinitrogen (N2) gas to ammonia (NH3) using the
nitrogenase Nitrogenases are enzymes () that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only fa ...
protein complex (Nif). Nitrogen fixation is essential to life because fixed inorganic nitrogen compounds are required for the biosynthesis of all nitrogen-containing
organic compounds In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The s ...
, such as amino acids and
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s, nucleoside triphosphates and nucleic acids. As part of the nitrogen cycle, it is essential for
agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people t ...
and the manufacture of
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
. It is also, indirectly, relevant to the manufacture of all nitrogen chemical compounds, which includes some explosives, pharmaceuticals, and dyes. Nitrogen fixation is carried out naturally in
soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...
by
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s termed diazotrophs that include
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
, such as ''
Azotobacter ''Azotobacter'' is a genus of usually motile, oval or spherical bacteria that form thick-walled cysts (and also has hard crust) and may produce large quantities of capsular slime. They are aerobic, free-living soil microbes that play an impo ...
,'' and archaea. Some nitrogen-fixing bacteria have symbiotic relationships with plant groups, especially legumes. Looser non-symbiotic relationships between diazotrophs and plants are often referred to as associative, as seen in nitrogen fixation on
rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and '' Porteresia'', both wild and domesticat ...
roots. Nitrogen fixation occurs between some
termite Termites are small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blatto ...
s and
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
. It occurs naturally in the air by means of NOx production by
lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an avera ...
. All biological reactions involving the process of nitrogen fixation are catalyzed by enzymes called
nitrogenase Nitrogenases are enzymes () that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only fa ...
s. These enzymes contain
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
, often with a second metal, usually molybdenum but sometimes vanadium.


History

Biological nitrogen fixation was discovered by Jean-Baptiste Boussingault in 1838. Later, in 1880, the process by which it happens was discovered by German
agronomist An agriculturist, agriculturalist, agrologist, or agronomist (abbreviated as agr.), is a professional in the science, practice, and management of agriculture and agribusiness. It is a regulated profession in Canada, India, the Philippines, the ...
Hermann Hellriegel and and was fully described by Dutch microbiologist
Martinus Beijerinck Martinus Willem Beijerinck (, 16 March 1851 – 1 January 1931) was a Dutch microbiologist and botanist who was one of the founders of virology and environmental microbiology. He is credited with the discovery of viruses, which he called "'' ...
. "The protracted investigations of the relation of plants to the acquisition of nitrogen begun by Saussure, Ville, Lawes and Gilbert and others culminated in the discovery of symbiotic fixation by Hellriegel and Wilfarth in 1887." "Experiments by Bossingault in 1855 and Pugh, Gilbert & Lawes in 1887 had shown that nitrogen did not enter the plant directly. The discovery of the role of nitrogen fixing bacteria by Herman Hellriegel and Herman Wilfarth in 1886-8 would open a new era of soil science." In 1901 Beijerinck showed that '' Azotobacter chroococcum'' was able to fix atmospheric nitrogen. This was the first species of the
azotobacter ''Azotobacter'' is a genus of usually motile, oval or spherical bacteria that form thick-walled cysts (and also has hard crust) and may produce large quantities of capsular slime. They are aerobic, free-living soil microbes that play an impo ...
genus, so-named by him. It is also the first known diazotroph, species that use diatomic nitrogen as a step in the complete nitrogen cycle.


Biological

Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is converted to ammonia by a
nitrogenase Nitrogenases are enzymes () that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only fa ...
enzyme. The overall reaction for BNF is: :N2 + 16ATP + 16H2O + 8e- + 8H+ -> 2NH3 +H2 + 16ADP + 16\text_i The process is coupled to the
hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolys ...
of 16 equivalents of ATP and is accompanied by the co-formation of one equivalent of . The conversion of into ammonia occurs at a
metal cluster In chemistry, an atom cluster (or simply cluster) is an ensemble of bound atoms or molecules that is intermediate in size between a simple molecule and a nanoparticle; that is, up to a few nanometers (nm) in diameter. The term ''microcluster ...
called
FeMoco FeMoco ( cofactor) is the primary cofactor of nitrogenase. Nitrogenase is the enzyme that catalyzes the conversion of atmospheric nitrogen molecules N2 into ammonia (NH3) through the process known as nitrogen fixation. Containing iron and moly ...
, an abbreviation for the iron- molybdenum cofactor. The mechanism proceeds via a series of
protonation In chemistry, protonation (or hydronation) is the adding of a proton (or hydron, or hydrogen cation), (H+) to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brønsted–Lowry acid ...
and reduction steps wherein the FeMoco active site hydrogenates the substrate. In free-living diazotrophs, nitrogenase-generated ammonia is assimilated into glutamate through the
glutamine synthetase Glutamine synthetase (GS) () is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine: Glutamate + ATP + NH3 → Glutamine + ADP + phosphate Glutam ...
/glutamate synthase pathway. The microbial
nif gene The ''nif'' genes are genes encoding enzymes involved in the fixation of atmospheric nitrogen into a form of nitrogen available to living organisms. The primary enzyme encoded by the ''nif'' genes is the nitrogenase complex which is in charge of ...
s required for nitrogen fixation are widely distributed in diverse environments. For example, decomposing wood, which generally has a low nitrogen content, has been shown to host a diazotrophic community. The bacteria enrich the wood substrate with nitrogen through fixation, thus enabling deadwood decomposition by fungi. Nitrogenases are rapidly degraded by oxygen. For this reason, many bacteria cease production of the enzyme in the presence of oxygen. Many nitrogen-fixing organisms exist only in
anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...
conditions, respiring to draw down oxygen levels, or binding the oxygen with a
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
such as leghemoglobin.


Importance of nitrogen

Atmospheric nitrogen is inaccessible to most organisms, because its triple covalent bond is very strong. Life takes up fixed nitrogen in various ways. Considering atom acquisition, for every 100 atoms of carbon, roughly 2 to 20 atoms of nitrogen are assimilated. The atomic ratio of carbon (C) : nitrogen (N) : phosphorus (P) observed on average in planktonic biomass was originally described by Alfred Redfield. The Redfield Ratio, the stoichiometric relationship between C:N:P atoms, is 106:16:1.


Nitrogenase

The protein complex nitrogenase is responsible for catalyzing the reduction of nitrogen gas (N2) to ammonia (NH3). In Cyanobacteria, this enzyme system is housed in a specialized cell called the
heterocyst Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as '' Nostoc punctiforme'', ''Cylindrospermum stagnale'', and ''Anabaena sphaerica''. They fix nitrogen fr ...
. The production of the nitrogenase complex is genetically regulated, and the activity of the protein complex is dependent on ambient oxygen concentrations, and intra- and extracellular concentrations of ammonia and oxidized nitrogen species (nitrate and nitrite). Additionally, the combined concentrations of both ammonium and nitrate are thought to inhibit NFix, specifically when intracellular concentrations of 2-oxoglutarate (2-OG) exceed a critical threshold. The specialized heterocyst cell is necessary for the performance of nitrogenase as a result of its sensitivity to ambient oxygen. Nitrogenase consist of two proteins, a catalytic iron-dependent protein, commonly referred to as MoFe protein and a reducing iron-only protein (Fe protein). There are three different iron dependent proteins, molybdenum-dependent, vanadium-dependent, and iron-only, with all three nitrogenase protein variations containing an iron protein component. Molybdenum-dependent nitrogenase is the most commonly present nitrogenase. The different types of nitrogenase can be determined by the specific iron protein component. Nitrogenase is highly conserved. Gene expression through DNA sequencing can distinguish which protein complex is present in the microorganism and potentially being express. Most frequently, the ''nif''H gene is used to identify the presence of molybdenum-dependent nitrogenase, followed by closely related nitrogenase reductases (component II) ''vnf''H and ''anf''H representing vanadium-dependent and iron-only nitrogenase, respectively. In studying the ecology and evolution of nitrogen-fixing bacteria, the ''nifH'' gene is the biomarker most widely used. ''nif''H has two similar genes ''anf''H and vnfH that also encode for the nitrogenase reductase component of the nitrogenase complex.


Microorganisms

Diazotrophs are widespread within domain
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
including cyanobacteria (e.g. the highly significant ''
Trichodesmium ''Trichodesmium'', also called sea sawdust, is a genus of Filamentation, filamentous cyanobacteria. They are found in nutrient poor tropical and subtropical ocean waters (particularly around Australia and in the Red Sea, where they were first des ...
'' and ''
Cyanothece ''Cyanothece'' is a genus of unicellular, diazotrophic, oxygenic photosynthesizing cyanobacteria. Modern organisms and cellular organization In 1976, Jiří Komárek defined the prokaryotic cyanobacteria genus ''Cyanothece'' as distinct from ' ...
''),
green sulfur bacteria The green sulfur bacteria are a phylum of obligately anaerobic photoautotrophic bacteria that metabolize sulfur. Green sulfur bacteria are nonmotile (except ''Chloroherpeton thalassium'', which may glide) and capable of anoxygenic photosynthe ...
, Azotobacteraceae, rhizobia and ''
Frankia ''Frankia'' is a genus of nitrogen-fixing bacteria that live in symbiosis with actinorhizal plants, similar to the ''Rhizobium'' bacteria found in the root nodules of legumes in the family Fabaceae. ''Frankia'' also initiate the forming of root ...
.'' Several obligately anaerobic bacteria fix nitrogen including many (but not all) '' Clostridium'' spp. Some archaea such as '' Methanosarcina acetivorans'' also fix nitrogen,. and several other methanogenic
taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
, are significant contributors to nitrogen fixation in oxygen-deficient soils. Cyanobacteria, commonly known as blue-green algae, inhabit nearly all illuminated environments on Earth and play key roles in the carbon and nitrogen cycle of the
biosphere The biosphere (from Greek βίος ''bíos'' "life" and σφαῖρα ''sphaira'' "sphere"), also known as the ecosphere (from Greek οἶκος ''oîkos'' "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also ...
. In general, cyanobacteria can use various inorganic and organic sources of combined nitrogen, such as nitrate, nitrite, ammonium,
urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...
, or some
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s. Several cyanobacteria strains are also capable of diazotrophic growth, an ability that may have been present in their last common ancestor in the
Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth during the Arc ...
eon. Nitrogen fixation not only naturally occurs in soils but also aquatic systems, including both freshwater and marine. Indeed, the amount of nitrogen fixed in the ocean is at least as much as that on land. The colonial marine cyanobacterium ''
Trichodesmium ''Trichodesmium'', also called sea sawdust, is a genus of Filamentation, filamentous cyanobacteria. They are found in nutrient poor tropical and subtropical ocean waters (particularly around Australia and in the Red Sea, where they were first des ...
'' is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen fixation in marine systems globally. Marine surface lichens and non-photosynthetic bacteria belonging in Proteobacteria and Planctomycetes fixate significant atmospheric nitrogen. Species of nitrogen fixing cyanobacteria in fresh waters include: '' Aphanizomenon'' and ''Dolichospermum'' (previously Anabaena). Such species have specialized cells called heterocytes, in which nitrogen fixation occurs via the nitrogenase enzyme.


Root nodule symbioses


Legume family

Plants that contribute to nitrogen fixation include those of the legume
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Fabaceae— with
taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
such as kudzu, clover,
soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu a ...
, alfalfa, lupin,
peanut The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible seeds. It is widely grown in the tropics and subtropics, important to both small and ...
and
rooibos Rooibos ( ; , meaning "red bush"), or ''Aspalathus linearis'', is a broom-like member of the plant family Fabaceae that grows in South Africa's fynbos biome. The leaves are used to make a herbal tea that is called rooibos (especially in S ...
. They contain symbiotic rhizobia bacteria within nodules in their
root systems In vascular plants, the roots are the plant organ, organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often b ...
, producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the fixed nitrogen is released, making it available to other plants; this helps to fertilize the
soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...
. The great majority of legumes have this association, but a few genera (e.g., ''
Styphnolobium ''Styphnolobium'' is a small genus of three or four species of small trees and shrubs in the subfamily Faboideae of the pea family Fabaceae, formerly included within a broader interpretation of the genus '' Sophora''. It was recently assigned to ...
'') do not. In many traditional farming practices, fields are rotated through various types of crops, which usually include one consisting mainly or entirely of clover. Fixation efficiency in soil is dependent on many factors, including the legume and air and soil conditions. For example, nitrogen fixation by red clover can range from .


Non-leguminous

The ability to fix nitrogen in nodules is present in actinorhizal plants such as
alder Alders are trees comprising the genus ''Alnus'' in the birch family Betulaceae. The genus comprises about 35 species of monoecious trees and shrubs, a few reaching a large size, distributed throughout the north temperate zone with a few sp ...
and bayberry, with the help of ''
Frankia ''Frankia'' is a genus of nitrogen-fixing bacteria that live in symbiosis with actinorhizal plants, similar to the ''Rhizobium'' bacteria found in the root nodules of legumes in the family Fabaceae. ''Frankia'' also initiate the forming of root ...
'' bacteria. They are found in 25 genera in the orders
Cucurbitales The Cucurbitales are an order of flowering plants, included in the rosid group of dicotyledons. This order mostly belongs to tropical areas, with limited presence in subtropical and temperate regions. The order includes shrubs and trees, togethe ...
,
Fagales The Fagales are an order of flowering plants, including some of the best-known trees. The order name is derived from genus ''Fagus'', beeches. They belong among the rosid group of dicotyledons. The families and genera currently included are as ...
and
Rosales Rosales () is an order of flowering plants. Peter F. Stevens (2001 onwards). "Rosales". At: Trees At: Angiosperm Phylogeny Website. At: Missouri Botanical Garden Website. (see ''External links'' below) It is sister to a clade consisting of Faga ...
, which together with the
Fabales The Fabales are an order of flowering plants included in the rosid group of the eudicots in the Angiosperm Phylogeny Group II classification system. In the APG II circumscription, this order includes the families Fabaceae or legumes (including ...
form a ''nitrogen-fixing clade'' of eurosids. The ability to fix nitrogen is not universally present in these families. For example, of 122 Rosaceae genera, only four fix nitrogen. Fabales were the first lineage to branch off this nitrogen-fixing clade; thus, the ability to fix nitrogen may be plesiomorphic and subsequently lost in most descendants of the original nitrogen-fixing plant; however, it may be that the basic genetic and physiological requirements were present in an incipient state in the
most recent common ancestor In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The ...
s of all these plants, but only evolved to full function in some of them. In addition, '' Trema'' (''Parasponia''), a tropical genus in the family
Cannabaceae Cannabaceae is a small family of flowering plants, known as the hemp family. As now circumscribed, the family includes about 170 species grouped in about 11 genera, including ''Cannabis'' (hemp), '' Humulus'' (hops) and '' Celtis'' (hackberries ...
, is unusually able to interact with rhizobia and form nitrogen-fixing nodules.


Other plant symbionts

Some other plants live in association with a
cyanobiont Cyanobionts are cyanobacteria that live in symbiosis with a wide range of organisms such as terrestrial or aquatic plants; as well as, algal and fungal species. They can reside within extracellular or intracellular structures of the host. In orde ...
(cyanobacteria such as '' Nostoc'') which fix nitrogen for them: * Some lichens such as '' Lobaria'' and '' Peltigera'' * Mosquito fern ('' Azolla'' species) *
Cycad Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male o ...
s *''
Gunnera ''Gunnera'' is the sole genus of herbaceous flowering plants in the family Gunneraceae, which contains 63 species. Some species in this genus, namely those in the subgenus ''Panke'', have extremely large leaves. Species in the genus are various ...
'' *'' Blasia'' (
liverwort The Marchantiophyta () are a division of non-vascular land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of ...
) * Hornworts Some symbiotic relationships involving agriculturally-important plants are: * Sugarcane and unclear
endophyte An endophyte is an endosymbiont, often a bacterium or fungus, that lives within a plant for at least part of its life cycle without causing apparent disease. Endophytes are ubiquitous and have been found in all species of plants studied to date; h ...
s * Foxtail millet and '' Azospirillum brasilense'' * Kallar grass and ''
Azoarcus ''Azoarcus'' is a genus of nitrogen-fixing bacteria. Species in this genus are usually found in contaminated water, as they are involved in the degradation of some contaminants, commonly inhabiting soil. These bacteria have also been found growi ...
'' sp. strain BH72 *
Rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and '' Porteresia'', both wild and domesticat ...
and '' Herbaspirillum seropedicae'' *
Wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
and ''
Klebsiella pneumoniae ''Klebsiella pneumoniae'' is a Gram-negative, non-motile, encapsulated, lactose- fermenting, facultative anaerobic, rod-shaped bacterium. It appears as a mucoid lactose fermenter on MacConkey agar. Although found in the normal flora of the mo ...
'' *
Maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...
landrace 'Sierra Mixe' / 'olotón' and various Bacteroidota and Pseudomonadota


Industrial processes


Historical

A method for nitrogen fixation was first described by
Henry Cavendish Henry Cavendish ( ; 10 October 1731 – 24 February 1810) was an English natural philosopher and scientist who was an important experimental and theoretical chemist and physicist. He is noted for his discovery of hydrogen, which he termed "infl ...
in 1784 using electric arcs reacting nitrogen and oxygen in air. This method was implemented in the Birkeland–Eyde process of 1903. The fixation of nitrogen by lightning is a very similar natural occurring process. The possibility that atmospheric nitrogen reacts with certain chemicals was first observed by Desfosses in 1828. He observed that mixtures of alkali metal oxides and carbon react with nitrogen at high temperatures. With the use of
barium carbonate Barium carbonate is the inorganic compound with the formula BaCO3. Like most alkaline earth metal carbonates, it is a white salt that is poorly soluble in water. It occurs as the mineral known as witherite. In a commercial sense, it is one of ...
as starting material, the first commercial process became available in the 1860s, developed by Margueritte and Sourdeval. The resulting barium cyanide reacts with steam, yielding ammonia. In 1898
Frank Frank or Franks may refer to: People * Frank (given name) * Frank (surname) * Franks (surname) * Franks, a medieval Germanic people * Frank, a term in the Muslim world for all western Europeans, particularly during the Crusades - see Farang Curr ...
and
Caro Caro may refer to: Places * Caro, Michigan, United States * Caro, Morbihan, France * Çaro, Pyrénées-Atlantiques, France Other uses * Caro (given name), including a list of people with the given name * Caro (surname), including a list of peo ...
developed what is known as the Frank–Caro process to fix nitrogen in the form of
calcium cyanamide Calcium cyanamide is the inorganic compound with the formula CaCN2. It is the calcium salt of the cyanamide () anion. This chemical is used as fertilizer and is commercially known as nitrolime. It was first synthesized in 1898 by Adolph Frank and ...
. The process was eclipsed by the
Haber process The Haber process, also called the Haber–Bosch process, is an artificial nitrogen fixation process and is the main industrial procedure for the production of ammonia today. It is named after its inventors, the German chemists Fritz Haber and ...
, which was discovered in 1909.


Haber process

The dominant industrial method for producing ammonia is the
Haber process The Haber process, also called the Haber–Bosch process, is an artificial nitrogen fixation process and is the main industrial procedure for the production of ammonia today. It is named after its inventors, the German chemists Fritz Haber and ...
also known as the Haber-Bosch process. Fertilizer production is now the largest source of human-produced fixed nitrogen in the terrestrial
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
. Ammonia is a required precursor to
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s, explosives, and other products. The Haber process requires high pressures (around 200 atm) and high temperatures (at least 400 °C), which are routine conditions for industrial catalysis. This process uses natural gas as a hydrogen source and air as a nitrogen source. The ammonia product has resulted in an intensification of nitrogen fertilizer globally and is credited with supporting the expansion of the human population from around 2 billion in the early 20th century to roughly 8 billion people now.


Homogeneous catalysis

Much research has been conducted on the discovery of catalysts for nitrogen fixation, often with the goal of lowering energy requirements. However, such research has thus far failed to approach the efficiency and ease of the Haber process. Many compounds react with atmospheric nitrogen to give
dinitrogen complex Transition metal dinitrogen complexes are coordination compounds that contain transition metals as ion centers the dinitrogen molecules (N2) as ligands. Historical background Transition metal complexes of N2 have been studied since 1965 when ...
es. The first dinitrogen
complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...
to be reported was ()2+. Some soluble complexes do catalyze nitrogen fixation.


Lightning

Nitrogen can be fixed by
lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an avera ...
converting nitrogen gas () and oxygen gas () in the atmosphere into (
nitrogen oxides Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds: Charge-neutral *Nitric oxide (NO), nitrogen(II) oxide, or nitrogen monoxide *Nitrogen dioxide (), nitrogen(IV) oxide * Nitrogen trioxide (), or ...
). The molecule is highly stable and nonreactive due to the
triple bond A triple bond in chemistry is a chemical bond between two atoms involving six bonding electrons instead of the usual two in a covalent single bond. Triple bonds are stronger than the equivalent single bonds or double bonds, with a bond order o ...
between the nitrogen atoms. Lightning produces enough energy and heat to break this bond allowing nitrogen atoms to react with oxygen, forming . These compounds cannot be used by plants, but as this molecule cools, it reacts with oxygen to form , which in turn reacts with water to produce (
nitrous acid Nitrous acid (molecular formula ) is a weak and monoprotic acid known only in solution, in the gas phase and in the form of nitrite () salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagent ...
) or (
nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
). When these acids seep into the soil, they make (nitrate), which is of use to plants.


See also

* Birkeland–Eyde process: an industrial fertilizer production process * Carbon fixation * Denitrification: an organic process of nitrogen release * George Washington Carver: an American botanist *
Heterocyst Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as '' Nostoc punctiforme'', ''Cylindrospermum stagnale'', and ''Anabaena sphaerica''. They fix nitrogen fr ...
*
Nitrification ''Nitrification'' is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate occurring through separate organisms or direct ammonia oxidation to nitrate in comammox bacteria. The transformation of am ...
: biological production of nitrogen * Nitrogen cycle: the flow and transformation of nitrogen through the environment * Nitrogen deficiency * Nitrogen fixation package for quantitative measurement of nitrogen fixation by plants *
Nitrogenase Nitrogenases are enzymes () that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only fa ...
: enzymes used by organisms to fix nitrogen *
Ostwald process The Ostwald process is a chemical process used for making nitric acid (HNO3). Wilhelm Ostwald developed the process, and he patented it in 1902. The Ostwald process is a mainstay of the modern chemical industry, and it provides the main raw materi ...
: a chemical process for making nitric acid ()


References


External links

* * *
Science History Institute The Science History Institute is an institution that preserves and promotes understanding of the history of science. Located in Philadelphia, Pennsylvania, it includes a library, museum, archive, research center and conference center. It was f ...
Digital Collections (Photographs depicting numerous stages of the nitrogen fixation process and the various equipment and apparatus used in the production of atmospheric nitrogen, including generators, compressors, filters, thermostats, and vacuum and blast furnaces).
Proposed Process for the Fixation of Atmospheric Nitrogen
, historical perspective,
Scientific American ''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it ...
, 13 July 1878, p. 21
A global ocean snapshot of nitrogen fixers by matching sequences to cells in the Tara Ocean
{{Authority control Nitrogen cycle Metabolism Plant physiology Soil biology