User:Natwo001/Nitrogen Fixation

Microorganisms (EDIT OF THE MICROORGANISM SECTION - ADDED TO ARTICLE)
Main article: Diazotroph

Diazotrophs are widespread within domain Bacteria including cyanobacteria (e.g. the highly significant Trichodesmium and Cyanothece), as well as green sulfur bacteria, Azotobacteraceae, rhizobia and Frankia. Several obligately anaerobic bacteria fix nitrogen including many (but not all) Clostridium spp. Some archaea also fix nitrogen, including several methanogenic taxa, which 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. In general, cyanobacteria can use various inorganic and organic sources of combined nitrogen, such as nitrate, nitrite, ammonium, urea, or some amino acids. Several cyanobacteria strains are also capable of diazotrophic growth, an ability that may have been present in their last common ancestor in the Archean eon. Nitrogen fixation not only naturally occurs in soils but also aquatic systems, including both freshwater and marine. Nitrogen fixation by cyanobacteria in coral reefs can fix twice as much nitrogen as on land—around 660 kg/ha/year. The colonial marine cyanobacterium Trichodesmium 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.

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Importance of Nitrogen (NEW MATERIAL TO ADD TO ARTICLE - NOT ADDED TO ARTICLE)

Nitrogen is an essential, naturally occurring, primary nutrient necessary for both cell formation and function. Nitrogen occurs in both inorganic and organic forms. Inorganic forms of nitrogen include, ammonia (NH3), ammonium (NH4+), nitrate (NO3-), nitrite (NO2-), and nitrogen gas (N2). Organic forms of nitrogen include but are not limited to protein, nucleic acids and urea. As a general overview, biomolecules such as proteins, enzymes, nucleic acids and chlorophyll contain nitrogen. Amino acids, the building blocks of all proteins contain N. Proteins encompass not only structural components such as muscle, tissue, and organs, but also metabolic components such as enzymes and hormones necessary for the functioning of all living things. Life’s blueprints and hereditary material, DNA and RNA, are polymers comprised of a series of nucleotides consisting of a nitrogen base. Although N is the fifth most abundant element, much of the comprised nitrogen is inaccessible to living organisms, as the majority is in the form of dinitrogen (N2gas) which makes up 80% of the Earth’s atmospheric composition deeming the atmosphere the largest reservoir for N (Delwiche 1983).The nitrogen requirements for life, depending on the organism highly varies and depends on evolutionary life history of the organism. Considering atom acquisition, for every 100 atoms of carbon, roughly 2 to 20 atoms of nitrogen are assimilated (Sterner and Elser 2002). The atomic ratio of Carbon(C): Nitrogen(N): Phosphorus(P) observed on average in planktonic biomass was originally discovered by Alfred Redfield in 1958. Now referred to as the Redfield Ratio, derives a stoichiometric relationship between C:N:P atoms in the ratio of 106:16:1 (Redfield 1958).

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Haber process (EDIT OF HABER PROCESS SECTION - NOT ADDED TO ARTICLE)
Main article: Haber process

The most common ammonia production method is the Haber process. The Haber-Bosch nitrogen reduction process for industrial fertilizer production revolutionized modern day technology (Smil 2004). Fertilizer production is now the largest source of human-produced fixed nitrogen in the terrestrial ecosystem. Ammonia is a required precursor to fertilizers, 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 byproduct has resulted in an intensification of nitrogen fertilizer globally (Glibert et al. 2014) and is accredited with supporting the expansion of human population from roughly 2 billion in the early 20th century to roughly 7 billion people presently (Erisman et al. 2008).

Much research has been conducted on the discovery of catalysts for nitrogen fixation, often with the goal of reducing 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 complexes. The first dinitrogen complex to be reported was Ru(NH 3)5(N2)2+.

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