Nitrogen ammonification

Ammonification (organic nitrogen NH3) Many microbes, especially bacteria... 

Ammonification is the breaking down of organic nitrogen compounds into NH3 or NHT... 

Besides nitrogen fixation, the only other major source of reduced nitrogen is the decomposition of soil or aquatic organic matter. This process is called ammonification. Heterotrophic bacteria are principally responsible for this. These organisms utilize organic compounds from dead plant or animal matter as a carbon source, and leave behind NH3 and NHJ, which can then be recycled by the biosphere. In some instances heterotrophic bacteria may incorporate a complete organic molecule into their own biomass. The majority of the NH3 produced in this way stays within the biosphere however, a small portion of it will be volatilized. In addition to this source, the breakdown of animal excreta also contributes to atmospheric... 

A simplified depiction of the marine nitrogen cycie iiiustrating redox and phase transitions mediated by microbes. The boxes contain the nitrogen species and its oxidation number. The arrows represent transformation reactions as foiiows (1) nitrogen fixation, (2) soiubiiization, (3) ammonification,... 

Ammonification The microbial process by which dissolved organic nitrogen is converted to ammonium. 

The involvement of HA during bacterial conversion of nitrate to NH3 (known also as the nitrate ammonification phase of the nitrogen cycle) has been studied at the molecular level as part of an effort to delineate the mechanism of conversion of nitrite to NH3 by a group of multiheme cytochromes of bacterial origin. The overall reduction reaction is depicted in equation 3 for cytochrome c-nitrite reductase " ... 

Nitrate and Ammonium. The transformations of nitrogen species may occur under suitable microbial catalysis (5, 36). Nitrate reduction may result in formation of either elemental nitrogen or ammonium. Mass balances over a whole lake have indicated the importance of the denitrification process for the elimination of nitrogen from lakes (37). The conditions for the dis-similative ammonification of nitrate are poorly known (36). Ammonium is also released by the mineralization of biomass. 

The nitrogen supplies on land consist of the assimilable nitrogen in the soil VS2 0.19-104tkm-2, in plants (12 1091), and living organisms (0.2 1091). A diversity of nitrogen fluxes is formed here of the processes of nitrification, denitrification, ammonification, fixation, and river run-off. The intensities of these fluxes depend on climatic conditions, temperature regime, moisture, as well as the chemical and physical properties of soil. Many qualitative and quantitative characteristics of these dependences have been described in the literature (Hellebrandt et al., 2003). Let us consider some of them. 

Figure 10.5 Major processes involved in the biogeochemical cycling of N in estuaries and the coastal ocean (1) biological N2 fixation (2) ammonia assimilation (3) nitrification (4) assimilatory NC>3 reduction (5) ammonification or N remineralization (6) ammonium oxidation (speculative at this time) (7) denitrification and dissimilatory NO3 reduction to NH4+ and (8) assimilation of dissolved organic nitrogen (DON). (Modified from Libes, 1992.)...

Ammonification process where NH3 or NH4+ is produced during the breakdown of organic nitrogen by organisms. 

Bacteria play an important role in the redox chemistry of nitrogen species in seawater. Starting with PON, the first step is remineralisation in which PON is converted to DON. The breakdown of some of the DON to DIN follows with the first product being NH3 the process is relatively rapid and known as ammonification. NH3 is protonated to a limited extent in seawater, giving rise to NH4 ions. Nitrification is the stepwise oxidation of NH4 to N02 and eventually to N03. Denitrification, the reduction of nitrogen species to N2, can occur under conditions of hypoxia or anoxia. In such cases, bacteria respire organic material using N03 and NO2 as electron acceptors. 

Figure 21.1 Microbial nitrogen cycling processes in sedimentary environments on a coral reef (A) nitrogen fixation (B) ammonification (C) nitrification (D) dissimilatory nitrate reduction and denitrification (E) assimilatory nitrite/nitrate reduction (F) ammonium immobilization and assimilation. Adapted from D Elia and Wiebe (1990). Anammox (the anaerobic oxidation of NH4" with NO2 yielding N2 ) is not represented, as it has not yet been shown to occur on coral reefs, but may be found to be important in reef sediments.

Mineralization is usually defined as the production of ammonium from soil organic matter. This is sometimes called ammonification, which is a less confusing term. Mineralization usually causes only a small fractionation ( l%o) between soil organic matter and soil ammonium. In general, the 6 N of soil ammonium is usually within a few per mil of the composition of total organic nitrogen in the soil. 

Nitrate reduction studies have focused overwhelmingly on denitrification at the expense of other NO sinks such as dissimulatory NO reduction to NH4 (also known as DNRA or nitrate ammonification). The ecological implications of reducing NOJ to NH4, versus N2 are vastly different because NH4 is more readily retained in the ecosystem, and it is a form that is readily assimilated by biota. Thus, DNRA contributes to eutrophication by reducing the quantity of fixed nitrogen that is returned to the atmosphere as N2. 

Figure 1 The processes of nitrogen fixation, assimilation, nitrification, decomposition, ammonification, and...

Nitrogen is transferred to the atmosphere by low- and high-temperature processes. The high-temperature processes are biomass combustion and fossil-fuel combustion the low-temperature processes are volatilization of gases from soils and waters and turbulent injection of particulate matter into the atmosphere. The gases are generated primarily as a result of microbial activity (e.g., nitrification, denitrihcation, and ammonification). 

For the most part, nitrogen cycles within the ocean have the same microbial processes as in the soil (Figure 1). BNF is the dominant source of new nitrogen to the ocean, with other smaller contributions coming from atmospheric deposition and riverine runoff. Ammonification, nitrification, uptake, and decomposition are all critical components. There are two primary removal mechanisms—denitrification and burial in marine... 

Oxidation of ammonia to nitrite, N02, and nitrate, N03, is called nitrification the reverse reaction is ammonification. Reduction from nitrite to nitrogen is called denitrification. All these reactions, and more, occur in enzyme systems, many of which include transition metals. A molybdenum enzyme, nitrate reductase, reduces nitrate to nitrite. Further reduction to ammonia seems to proceed by 2-electron steps, through an uncertain intermediate with a -fl oxidation state (possibly hyponitrite, N202 ) and hydroxylamine ... 

Interestingly, nitrification is a process that actually generates acidity, equivalent to two H+ ions for every ion of NO3 produced by the oxidation of NH4+. However, the ammonification of organic nitrogen to ammonium consumes one H+, as does the uptake of nitrate from soil by plant roots. Therefore, nitrification only acidifies soils if the ammonium substrate is added directly, for example through fertilization or by atmospheric deposition, or if the nitrate is not taken up by plants and leaches from the soil. 

Ammonification—The microbial conversion of organic nitrogen to ammonium in soil or water. 

Ammonification is the process by which the organically bound nitrogen of microbial, plant, and animal biomass is recycled after their death. Ammonification is carried out by a diverse array of microorganisms that perform ecological decay services, and its product is ammonia or ammonium ion. Ammonium is a suitable source of nutrition for many species of plants, especially those living in acidic soils. However, most plants cannot utilize ammonium effectively, and they require nitrate as their essential source of nitrogen nutrition. 

Fig. 3.17 Summary of the nitrogen cycle (oxidation states of nitrogen shown in parentheses). Ammonium assimilation and ammonification can occur in oxic and anoxic environments, as can nitrogen fixation (although the most prolific bacteria are aerobes).

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