Nitrogen Cycle

Nitrogen cycle is not only a biological cycle; it is also a geographical cycle. It illustrates the way atmospheric nitrogen and other nitrogenous compounds go through a transformation. About 70% of the earth’s atmosphere is made up of nitrogen. Thus we can say that earth’s atmosphere is the largest source of nitrogen. This nitrogen becomes a part of many biological processes and is also part of most essential components that serve as the foundation stones of life like DNA, RNA, proteins and the like. All living beings need nitrogen to sustain life on earth surface. However, the nitrogen that is present in the atmosphere is not usable in its form by any living organism.

Nitrogen Cycle: How is atmospheric nitrogen converted?

Leguminous plants are plants that have nodules in their roots so that they can absorb atmospheric nitrogen. This process is called Nitrogen fixation, which is necessary otherwise it would be impossible for living beings to use atmospheric nitrogen. Fixation also occurs when the atmospheric temperature is high and also due to lightening since this is when the nitrogen is converted to nitrogen oxides. The chances of such nitrogen fixation are very less.

The bacteria present in the nodules in the leguminous plants contain nitrogenase enzymes that help in the reaction of hydrogen and nitrogen, which helps to get ammonia. Ammonia is further is converted into organic compounds. This is the juncture where the leguminous plants establish a symbiotic relationship with the bacteria present in the nodules. Bacteria help to produce ammonia and in return they take carbohydrate from the plant. Such leguminous plants can be planted in soils that have poor fertility so that atmospheric nitrogen can be trapped in the soil and it benefits the plant.

This is how plants receive their share of nitrogen but in case of animals, irrespective of the class and species, they receive it only by eating these plants, thus making it a part of the food chain. This is the best way for animals to take in nitrogen since the other ways can have some harmful effects as well like if nitrogen dissolves in water, which it does at times, it can effect the oxygen level in the blood of an infant and also lead to the disorders like blue-baby syndrome. It can also be a threat to the aquatic life since nitrogen enhances the growth of algae which increases the oxygen demand, and that might lead to the death of aquatic animals.

Process of Nitrogen Cycle

• First the atmospheric is converted into a form that can be utilized by living beings, which can be done by Nitrogen fixation (biological or Industrial) or the combustion of fossil fuels.
• Once it is converted, it is absorbed by the plant body, which is disintegrated in the system. Nitrogen is converted into ions of nitrite and ammonium, which are in turn converted into amino acids, nucleic acids and most importantly chlorophyll.
• Now the plant, throughout its life span converts nitrogen and uses it but when it dies, or even if an animal which has nitrogen in its body dies, it gets mixed with the soil in the form of organic matter. This nitrogen is again converted into ammonia by bacteria present in the soil; hence the process is called ammonification.
• The ammonia is then converted into nitrates with the help of bacteria in the soil. It is oxidized and then the ammonia is converted into nitrites.
• Once converted into nitrites, these nitrites are again converted into atmospheric nitrogen, the form they were prior to fixation and this achieved with the help of bacteria like Pseudomonas and Clostridum.

Thus inert atmospheric nitrogen that was converted into usable nitrogen is again released into atmosphere. This is the process of Nitrogen Cycle that establishes a balance between the nitrogen that can be used and inert nitrogen in the atmosphere of earth.