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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.
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
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]
In specific plant/root symbiotic relationships, the plant root secretes flavonoids into the soil which is sensed by microbes, where these microbes release nod factors to the plant root which promotes the infection of the plant root. These unique microbes carry out nitrogen fixation in root nodules, which supplies nutrients to the plant.
[52] [53] Nitrogen gases and aerosols can be directly toxic to certain plant species, affecting the aboveground physiology and growth of plants near large point sources of nitrogen pollution. Changes to plant species may also occur as nitrogen compound accumulation increases availability in a given ecosystem, eventually changing the species ...