Nitrogen Cycle
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 NH4 is than converted into nitrite which is later converted into nitrate, and the process further repeats itself. 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.
Subsection 2a
Subsection 2b
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-
Subsection 3a
Subsection 3b
NH4+ to NO3-
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
Subsection 4a
Subsection 4b
NO3- to Atmospheric N2, happens in anaerobic conditions
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
Topic of your choice.
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
Enter summaries of recent research here--at least three required
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
"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
