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Nitrogen is a fundamental nutrient in agriculture, playing a crucial role in plant growth and development. It is an essential component of proteins, enzymes, chlorophyll, and nucleic acids, all of which are essential for various metabolic processes within plants. [2]
Nitrogen is the most critical element obtained by plants from the soil, to the exception of moist tropical forests where phosphorus is the limiting soil nutrient, [36] and nitrogen deficiency often limits plant growth. [37] Plants can use nitrogen as either the ammonium cation (NH 4 +) or the anion nitrate (NO 3 −).
Most of the nitrogen taken up by plants is from the soil in the forms of NO − 3, although in acid environments such as boreal forests where nitrification is less likely to occur, ammonium NH + 4 is more likely to be the dominating source of nitrogen. [49] Amino acids and proteins can only be built from NH + 4, so NO − 3 must be reduced.
Within legume root nodules, nitrogen gas (N 2) from the atmosphere is converted into ammonia (NH 3), which is then assimilated into amino acids (the building blocks of proteins), nucleotides (the building blocks of DNA and RNA as well as the important energy molecule ATP), and other cellular constituents such as vitamins, flavones, and hormones.
Nitrogen is a component of amino acids and is released upon deamination. It is typically released in the form of ammonia, which may be used by plants or microbes in the surrounding environment, converted to nitrate, or can accumulate in soil (if the body is located on top of or within soil). [4]
Plants that contribute to nitrogen fixation include those of the legume family—Fabaceae— with taxa such as kudzu, clover, soybean, alfalfa, lupin, peanut and rooibos. [45] They contain symbiotic rhizobia bacteria within nodules in their root systems, producing nitrogen compounds that help the plant to grow and compete with other plants. [58]
Non-protein amino acids (NPAAs) Nitrogen-containing 700 NPAAs are produced by specific plant families such as Leguminosae, Cucurbitaceae, Sapindaceae, Aceraceae and Hippocastanaceae. Examples: Azatyrosine, Canavanine: Amines: Nitrogen-containing 100 Cyanogenic glycosides: Nitrogen-containing 60 Amygdalin, Dhurrin, Linamarin, Lotaustralin, Prunasin
These plants are then digested by animals who use the nitrogen compounds to synthesise their proteins and excrete nitrogen-bearing waste. Finally, these organisms die and decompose, undergoing bacterial and environmental oxidation and denitrification , returning free dinitrogen to the atmosphere.