Nitrification - Nitrification As A Bacterial Process, Environmental Influences On Nitrification, Humans And Nitrification
nitrate nitrite nitrogen ammonium
Nitrification is an aerobic microbial process by which specialized bacteria oxidize ammonium to nitrite and then to nitrate. Nitrification is a very important part of the nitrogen cycle, because for most plants nitrate is the preferred chemical form of nitrogen uptake from soil or water.
Nitrification is a two-step process. The first stage is the oxidation of ammonium (NH4+) to nitrite (NO2-), a function carried out by bacteria in the genus Nitrosomonas. The nitrite formed is rapidly oxidized to nitrate (NO3-) by bacteria in the genus Nitrobacter. Because nitrate and nitrite are much more mobile in soils than ammonium, nitrification can be viewed as a process that mobilizes nitrogen, making it more available for plant uptake but potentially allowing it to leach from the ecosystem. The latter is an undesirable attribute of nitrification because fixed nitrogen is an important component of the nutrient capital of ecosystems. In addition, large concentrations of nitrate or nitrite can pollute groundwater and surface waters.
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Nitrification is an autotrophic process during which bacteria couple energy release from the oxidation of ammonium with the biosynthesis of simple inorganic molecules such as carbon dioxide and water into organic compounds. Because chemical energy is being tapped by the bacteria, nitrification is known as a chemoautotrophic process rather than photoautotrophic, as when green plants utilize sunligh…
The genera of bacteria that are responsible for nitrification are highly sensitive to acidity, so this process does not occur at significant rates in acidic soil or water, especially in those with pH less than 5.5. Plants that grow in acidic habitats such as bogs and some forests must be capable of utilizing ammonium as their source of nitrogen nutrition because nitrate is not available in those h…
The use of nitrogen-containing fertilizers in agriculture has a strong influence on nitrification and on the nitrogen cycle more broadly. Rates of fertilization in intensive agricultural systems often exceed 500 kg of nitrogen per hectare per year. Much of the nitrogen addition occurs as ammonia or ammonium which is the substrate for nitrification, so this process can occur very rapidly, and nitra…
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