Process



 Nitrogen cycle

Nitrogen (N), the building blocks of life, is an essential component of DNA, RNA, and proteins. All organisms require nitrogen to live and grow. Although most of the air we breathe is N2, most of the nitrogen in the atmosphere is not available for use by the agencies. The reason is that because the strong triple bond between atoms N in the N2 molecules, nitrogen is relatively inert. In fact, for plants and animals can use nitrogen, N2 gas must first be converted to a chemical form available as ammonium (NH4 +), nitrate (NO3-), or organic nitrogen (eg urea - ( NH3) 2CO). The inert nature of N 2 means that biologically available nitrogen is often scarce in natural ecosystems. This limits the plant growth and biomass accumulation. Nitrogen is an incredibly versatile element that exists in both inorganic and organic, while in many different oxidation states. The movement of nitrogen between the atmosphere, biosphere and geosphere in different forms is described in the nitrogen cycle (Figure 1). This is one of the most important biogeochemical cycles. Like the carbon cycle, nitrogen cycle consists of several banks or storage bags of nitrogen and processes by which the stock exchange nitrogen (arrows).
  The main processes that make up the nitrogen cycle that passes through the biosphere, atmosphere and geosphere are five: the fixation of nitrogen, making nitrogen (growth of organisms), nitrogen mineralization (decay), nitrification and denitrification. Microorganisms, particularly bacteria, play an important role in all the major transformations of nitrogen. As microbial mediation processes, these nitrogen transformations generally occur faster than geological processes such as plate movement is a purely physical process that is part of the carbon cycle. In the case of microbial mediation processes, speed is affected by environmental factors such as temperature, humidity and availability of resources that influence microbial activity. Nitrogen Fixation NH4 + N2 Nitrogen fixation is a process in which the N2 becomes ammonium. This is essential because it is the only way in which agencies can obtain nitrogen directly from the atmosphere. Some bacteria, eg Rhizobium, are the only organisms that fix nitrogen through metabolic processes. This symbiosis occurs in a well-known in the family of legumes (eg beans, peas and clover). In this respect, the nitrogen fixing bacteria inhabiting the root nodules of legumes (Figure 2) and receive carbohydrates and a favorable environment of their host plant in exchange for part of the nitrogen fixing them. There are also nitrogen-fixing bacteria that exist without plant hosts. These are called nitrogen fixing free of restrictions. In aquatic environments, blue-green algae (actually a bacteria called cyanobacteria) is an important nitrogen fixing free of restrictions. In addition to the nitrogen fixing bacteria, natural high-energy events such as lightning, forest fires and even lava flows can cause the fixation of small but significant amounts of nitrogen. (Figure 3). The high energy of these natural phenomena can break the triple bonds of the molecules of N2, achievable by individual atoms of N for the chemical transformation. During the last century, humans have become stationary sources of nitrogen, as important as all natural sources combined nitrogen, fossil fuel burning, using synthetic nitrogen fertilizers and cultivating nitrogen-fixing legumes. Through these actvidades, humans have doubled the amount of fixed nitrogen is dispersed into the biosphere each year (Figure 3). Then we discuss the consequences of this process.
  Nitrogen making NH4 + Organic N Ammonia produced by nitrogen fixing bacteria is usually quickly incorporated into protein and other organic nitrogen compounds, either by the host plant for the same bacteria, or another soil organism. When organisms nearer the top of the food chain (like us!) Eat, use the nitrogen that has been initially set by the nitrogen fixing bacteria. Nitrogen mineralization Organic N NH4 + After the nitrogen is incorporated into organic matter, often converted back into inorganic nitrogen through a process called nitrogen mineralization, also known as disintegration. When organisms die, the decomposing materials (such as bacteria and fungi) consume the organic matter and lead to the decomposition process. During this process, a significant amount of nitrogen contained within the dead organism is converted to ammonium. Once nitrogen is in ammonium form is also available for use by plants or for further processing into nitrate (NO3-) through a process called nitrification. Nitrification NH4 + NO3-Part of the ammonium produced by decomposition is converted to nitrate through a process called nitrification. The bacteria that perform this reaction get energy from itself. Nitrification requires the presence of oxygen. Consequently, nitrification can happen only in oxygen-rich environments, such as water circulating or flowing and the surface layers of soil and sediment. The process of nitrification has some important consequences. Ammonium ions are positively charged and therefore stick to particles and soil organic matter are negatively charged. The positive charge prevents ammonium nitrogen is swept (or leachate) from the soil by rain. On the other hand, the nitrate ion with negative charge is not retained in soil particles and can be wiped off the soil profile. This leads to a decrease in soil fertility and nitrate enrichment of running water from the surface and subsurface. The Denitrification NO3-N2 + N2O Through denitrification, oxidized forms of nitrogen such as nitrate and nitrite (NO2-) are converted to dinitrogen (N2) and to a lesser extent, nitrous oxide gas. Denitrification is an anaerobic process carried out by bacteria that denitrifica, which converts nitrate to dinitrogen in the following sequence: NO3-NO2-N2 N2O NO. Nitric oxide and nitrous oxide gases are important for the environment. Nitric oxide (NO) helps to form smog, and nitrous oxide (N2O) is an important greenhouse gas, thus contributing to global climate change. Once conviete in dinitrogen, nitrogen is unlikely to be converted into a biologically available because it is a gas and is rapidly lost into the atmosphere. Denitrification is the only nitrogen transformation that removes nitrogen from the ecosystem (which is essentially irreversible), and about balancing the amount of nitrogen fixed by nitrogen fixing described above. 

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