Nitrogen Cycle: Difference between revisions

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===Nitrogen Immobilization===
===Nitrogen Immobilization===
Immobilization is the conversion of ammonium to organic nitrogen, primarily as a result of the assimilation of ammonium by the microbial biomass. Heterotrophic microbes and other organisms assimilate ammonium to build up biomass.  
Immobilization is the conversion of ammonium to organic nitrogen, primarily as a result of the assimilation of ammonium by the microbial biomass. Heterotrophic microbes and other organisms assimilate ammonium to build up biomass.  
===C/N Ratios===


===Nitrification===
===Nitrification===

Revision as of 19:51, 8 March 2008

Nitrogen cycle & Greenhouse Gases

The nitrogen cycle is an important chemical cycle which occurs in the ecosystem. The nitrogen cycle begins when atmospheric N2 is transformed by organisms to NH4. This process is known as mineralization, when organic nitrogen is transformed into inorganic nitrogen. This NH4 is than converted into nitrite which is later converted into nitrate, and the process further repeats itself. This process is known as nitrfication, and is carried out mainly my nitrifying bacteria such as nitrococcus, and nitrobacter. Nitrification occurs when the environment is aerobic. When the environment is anaerobic the nitrate undergoes denitrification which can have severe consequences with regards to the atmophere. Denitrification is when nitrate gets converted into atmospheric nitrogen which is a greenhouse gas. Immobilization is another step in this cycle and is the conversion of nitrate to organic nitrogen. The nitrogen cycle is important because it results in important compounds being produced which are essential for proper growth of plants and other organisms.

Nitrogen cycle processes

Nitrogen is an essential nutrient for all life on earth. It is present in various forms such as dinitrogen gas, organic nitrogen, and ammonium and nitrate ions. Microbially mediated processes transform nitrogen form one form to another. These transformations include nitrogen fixation (transformation of dinitrogen to ammonia), ammonification/ mineralization (conversion of organic nitrogen to ammonium), nitrification (conversion of ammonium to nitrate), immobilization (assimilation), and denitrification (reduction of nitrate to gaseous oxide and dinitrogen)


Nitrogen fixation

Atmospheric nitrogen (N2) is abundant, but unavailable for biological activity due to the high energy required to break the triple bond. In nitrogen fixation, atmospheric nitrogen is reduced to biologically useful ammonia (NH3) by the activity of prokaryotes utilizing a nitrogenase.

Chemistry

The reaction catalyzed by nitrogenase is N2 + 8H+ + 8e- ---> 2NH3 + H2. Ammonia produced in this way is rapidly protonated to NH4+. Nitrogenases are irreversibly inhibited by exposure to O2, and thus organisms must take steps to prevent this. Some organisms, such as azotobacter protect their nitrogenases with a thick capsule that slows oxygen diffusion. Others, such as the cyanobacteria nostoc form special cells with thick cell walls to exclude oxygen, allowing the cell to provide fixed nitrogen to its neighbors. Alternative nitrogenases do exist that are not deactivated by oxygen, but they are found in a relatively small number of organisms.

Ecology

Nitrogen fixed by prokaryotes constitutes the vast majority of all biologically active nitrogen on the planet. Nitrogen-fixers may be aerobic or anaerobic, and may be free-living or in a symbiotic relationship with a plant.

Nitrogen Mineralization

Nitrogen mineralization is the sum of concurrent ammonium production and consumption processes. It is sometimes used in a generic sense for the production of inorganic nitrogen, both ammonium and nitrate (Sylvia et al, 2005).

Ammonification or gross nitrogen mineralization is the conversion of organic-nitrogen compounds to ammonium. This process is mediated by heterotrophic microbes. Production of ammonium involves several steps. First organic nitrogen is broken down by extracellular enzyme. Then the resulting products pass across cell membrane and are metabolized, resulting in ammonium production, which release into the soil solution.

Naturally, ammonification and nitrogen immobilization are coincidence. There are several factors influences whether there is net production or consumption by microorganisms in soil. The general principle is that net production occurs when nitrogen is not limiting.

Nitrogen Immobilization

Immobilization is the conversion of ammonium to organic nitrogen, primarily as a result of the assimilation of ammonium by the microbial biomass. Heterotrophic microbes and other organisms assimilate ammonium to build up biomass.

C/N Ratios

Nitrification

Nitrification is the microbial production of nitrate from the oxidation of reduced nitrogen compound. This process is two-step process. The first step of lithoautotrophic nitrification is ammonia oxidation, the conversion of ammonium to nitrite by ammonia-oxidizing bacteria of Nitroso- genera. Then nitrite is oxidized to nitrate by the nitrite-oxidizing bacteria of the Nitro- genera (Sylvia et al., 2005).

Ammonia Oxidation: NH3 + 1.5 O2 --> NO2- + H+ +H2O

Nitrite Oxidation: NO2- + H2O --> NO3- + 2H+ + 2e-

Denitrification

Denitrification is the conversion of nitrate to nitrogen gas in presence of low oxygen (Sylvia et al., 2005). Nitrates are reduced to nitrites, and then the reduction of nitrites to nitrogen gas occurs. Most microorganisms who mediate this process are facultative anaerobic organoheterotrophs. Because this process is carried out under anoxic or near anaerobic conditions, to create this condition in the experiment, soils were flooded by water. The overall or reaction is:

2 NO3- + 5H2 + 2H+ --> N2 + 6 H2O


Key Microorganisms in Nitrogen cycle

Bacteria involved- nitraosomas, nitrobacter, e.g. Nitrobacter hamburgensis, Nitrobacter winogradskyi,are key players in the nitrogen cycle

Identify and describe some microorganisms involved. Do they already have their own microbewiki pages? Add links. Create at least one page for a microbe relevant to your topic. Template will appear soon.

Greenhouse gases

Nitrous oxide or "laughing gas" is the form of nitrogen that is a green house gas. Along with carbon dioxide, ozone, methane, water vapor, and halocarbons, nitrous oxide causes the blanket of air surrounding the earth to thicken; thus warming up the earth itself. This phenomenon has been dubbed "Global Warming" and understanding it's causes is key to preventing the mass destruction that will happen if green house gases remain unchecked. (The Environmental Literacy Council)

Current Research

The Center of Limnology is currently studying the rise in organic nitrogen availability to microbes. Their findings may lead to an analysis of the consequences of anthropogenic nitrogen enrichment watersheds. To learn more visit their website at http://cires.colorado.edu/limnology/research/

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

"Green House Gasses." The Environmental Literacy Council. 2002. Last Updated May 2007. http://www.enviroliteracy.org/article.php/428.html

Edited by student of Kate Scow