What is nitrogen cycle? Explain the steps involved in it.
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“Nitrogen Cycle is a biogeochemical process which transforms the inert nitrogen present in the atmosphere to a more usable form for living organisms.”
Process of Nitrogen Cycle consists of the following steps – Nitrogen fixation, Nitrification, Assimilation, Ammonification, and Denitrification. These processes take place in several stages and are explained below:
1)Stages of Nitrogen Cycle
Process of Nitrogen Cycle consists of the following steps – Nitrogen fixation, Nitrification, Assimilation, Ammonification, and Denitrification. These processes take place in several stages and are explained below:
2)Nitrogen fixation
It is the initial step of the nitrogen cycle. Here, Atmospheric nitrogen (N2)which is primarily available in an inert form, is converted into the usable form -ammonia (NH3).
During the process of Nitrogen fixation, the inert form of nitrogen gas is deposited into soils from the atmosphere and surface waters, mainly through precipitation. Later, the nitrogen undergoes a set of changes, in which two nitrogen atoms get separated and combines with hydrogen to form ammonia (NH4+).
The entire process of Nitrogen fixation is completed by symbiotic bacteria which are known as Diazotrophs. Azotobacter and Rhizobium also have a major role in this process. These bacteria consist of a nitrogenase enzyme which has the capability to combine gaseous nitrogen with hydrogen to form ammonia.
Nitrogen fixation can occur either by the atmospheric fixation- which involves lightening or industrial fixation by manufacturing ammonia under high temperature and pressure condition. This can also be fixed through man-made processes, primarily industrial processes that create ammonia and nitrogen-rich fertilisers.
3)Nitrification
In this process, the ammonia is converted into nitrate by the presence of bacteria in the soil. Nitrites are formed by the oxidation of Ammonia with the help of Nitrosomonas bacterium species. Later, the produced nitrites are converted into nitrates by Nitrobacter. This conversion is very important as ammonia gas is toxic for plants.
The reaction involved in the process of Nitrification is as follows:
2NH4+ + 3O2 → 2NO2– + 4H+ + 2H2O
2NO2– + O2 → 2NO3–
4)Assimilation
Primary producers – plants take in the nitrogen compounds from the soil with the help of their roots, which are available in the form of ammonia, nitrite ions, nitrate ions or ammonium ions and are used in the formation of the plant and animal proteins. This way, it enters the food web when the primary consumers eat the plants.
5)Ammonification
When plants or animal die, the nitrogen present in the organic matter is released back into the soil. The decomposers, namely bacteria or fungi present in the soil, convert the organic matter back into ammonium. This process of decomposition produces ammonia which is further used for other biological processes.
6)Denitrification
Denitrification is the process in which the nitrogen compounds makes its way back into the atmosphere by converting nitrate (NO3-) into gaseous nitrogen (N). This process of the nitrogen cycle is the final stage and occurs in the absence of oxygen. Denitrification is carried out by the denitrifying bacterial species- Clostridium and Pseudomonas, which will process nitrate to gain oxygen and gives out free nitrogen gas as a byproduct.
Q-:Why is nitrogen important for life?
Nitrogen constitutes many cellular components and is essential in many biological processes. For instance, the amino acids contain nitrogen and form building blocks that make up various components of the human body such as hair, tissues and muscles.
Q-:Why do plants need nitrogen?
Plants need nitrogen as this element is an important component of chlorophyll. Consequently, chlorophyll is vital for the process of photosynthesis, so lack of nitrogen can cause deficiency disorders, stunted growth and other abnormalities.