Circulation of chemical element in the biosphere is called a biogeochemical cycle. The crucial role in circulation of nitrogen in the nature is played by living organisms. What transformations are undergone by this biogenous element in the circulation?
Nitrogen in the atmosphere
From the chemical point of view nitrogen – typical nonmetal. Under usual conditions atmospheric nitrogen is the gas without color and a smell consisting of diatomic molecules N2. In the nature nitrogen is presented by two stable isotopes: nitrogen with the atomic mass of 14 (99.6%) and nitrogen with the atomic mass of 15 (0.4%).
As a part of atmospheric air nitrogen is the main gas component and occupies 78% of volume.
Nitrogen as biogenous element
Biogenous ("giving life") call the elements necessary for life. The chemical basis of fabrics of living organisms is formed by 9 makrotrofny substances: carbon, hydrogen, nitrogen, oxygen, potassium, calcium, phosphorus, magnesium and sulfur. Nitrogen is a part of plants and animals in the form of proteins therefore its circulation in the nature is very important for maintenance of life on Earth.
Binding of atmospheric nitrogen
Binding, or nitrogen fixing, process of its transformation into a form, usvoyaemy plants and animals is called. It can occur in two ways: under the influence of electric discharges or by means of bacteria. During lightning discharges a part of atmospheric nitrogen and oxygen connects to formation of nitrogen oxides: N2 + O2 = 2 NO – Q, 2 NO + O2 = 2NO2. These oxides are dissolved in water and form the diluted nitric acid: 2NO2 + H2O = HNO2 + HNO3 (on cold), 3NO2 + H2O = 2HNO3 + NO (when heating). Nitric acid already, in turn, forms nitrates in the soil which can appear there also from the ammonium connections which are present at the soil (excrements of animals, organic chemistry of dead bodies) under the influence of special bacteria.
Nitrates can be brought in addition in the soil by the person in the form of fertilizers.
Plants acquire nitrates from the soil through the root system and use them for synthesis of proteins. Animals use plants and produce own proteins. After death of plants and animal their proteins decay, forming ammonium and its connections. Eventually these connections under the influence of putrefactive bacteria turn into the nitrates remaining in the soil and atmospheric nitrogen. Except lightnings during a thunderstorm, there is also other way of fixing of atmospheric nitrogen and its transformation into soil nitrates – activity of nitrogen-fixing bacteria. Distinguish from them free living nitrifiers in the soil and klubenkovy bacteria living on roots of bean plants (for this reason the cultivation of beans on the site promotes increase in fertility of the soil). Under the influence of these microorganisms, atmospheric nitrogen directly turns into nitrates and becomes available to assimilation by plants.