Nitrogen Cycle Explained – Definition, Stages and Importance

A continuous sequence of natural activities known as the nitrogen cycle, which occurs when nitrogen moves from the air to the soil to organisms and then back to the air or soil. The primary nitrogen cycle processes include nitrogen fixation, nitrification, degradation, and denitrification. 

Nitrogen Cycle 

The biogeochemical process known as the nitrogen cycle is responsible for converting the inert form of nitrogen found in the atmosphere into a form that can be used by various forms of life. In addition, nitrogen is a nutrient that plants need in significant amounts. On the other hand, plants and animals are unable to directly use the abundant nitrogen that is found in the atmosphere. Keep reading if you’re interested in learning how the nitrogen cycle supplies plants and other living things with nitrogen that may be used. 

What is the Nitrogen Cycle? 

The nitrogen cycle is a biogeochemical process that involves the transformation of nitrogen into a number of different forms before its eventual return to the atmosphere through the soil and the organisms that live in it. 

Several different processes, including nitrogen fixation, nitrification, denitrification, degradation, and putrefaction, are all a part of this system. 

There are both organic and inorganic variations of nitrogen gas. Organic nitrogen is a kind of nitrogen that may be found in living things and is passed down the food chain when one living thing consumes another living thing. 

There is a possibility that the atmosphere contains a significant amount of inorganic nitrogen. This nitrogen is made accessible to plants by symbiotic bacteria that are capable of converting inert nitrogen into forms that are helpful to plants, such as nitrites and nitrates. 

In order to keep the natural balance of the ecosystem intact, nitrogen passes through a number of different changes. In addition, this process has an impact on a wide range of ecosystems, with the marine nitrogen cycle being one of the most intricate biogeochemical cycles. 

Stages of Nitrogen Cycle 

Nitrogen fixation, Nitrification, Assimilation, Ammonification, and Denitrification are the stages that make up the Nitrogen Cycle. 

Nitrogen Fixation Process 

This phase marks the beginning of the nitrogen cycle. In the course of this process, the inert form of atmospheric nitrogen, known as N2, is converted into the helpful form, known as ammonia (NH3). 

The process of nitrogen fixation involves the deposition of an inert form of nitrogen gas into soils from the atmosphere and surface waters, the majority of which is accomplished via precipitation. 

The last step in the process of nitrogen fixation is carried out by symbiotic bacteria that are known as diazotrophs. In addition to that, Azotobacter and Rhizobium also play significant roles in this process. These bacteria have an enzyme called nitrogenase, which has the ability to create ammonia by mixing gaseous nitrogen with hydrogen. 

Fixation of nitrogen may occur in one of two ways: either naturally in the atmosphere, which can include lightning, or industrially, which needs the creation of ammonia under conditions of high temperature and pressure. Both of these processes require the nitrogen to be in a stable form. 

In addition, there is the potential for assistance from human-made processes, particularly industrial processes that generate ammonia and nitrogen-rich fertilisers. 

Types of Nitrogen Fixation 

1. The natural process known as atmospheric fixation involves the splitting of nitrogen into nitrogen oxides by the energy of lightning. These nitrogen oxides are subsequently used by plants. 
2. The anthropogenic process of industrial nitrogen fixation is a substitute for natural nitrogen fixation that makes use of ammonia as a catalyst. Ammonia is the product that results from the straightforward combining of nitrogen and hydrogen. After that, it is processed into urea and several other types of fertiliser. 
3. Biological nitrogen fixation: It is well known that plants and animals do not take nitrogen in the form it is found in the atmosphere directly. Bacteria like Rhizobium and blue-green algae are responsible for the transformation of an inert form of nitrogen into compounds that can be utilised more easily. Microorganisms like this are responsible for repairing broken nitrogen molecules in the soil. 

Nitrification 

During this process, the presence of microorganisms in the soil is responsible for converting ammonia to nitrate. Nitrites are produced when ammonia is oxidised with the assistance of Nitrosomonas bacteria. This process creates nitrates. The nitrites that are produced are subsequently converted into nitrates by nitrobacter. This conversion is very necessary since ammonia gas is detrimental to the health of plants. The following is an example of the reaction that takes place during the process of nitrification: 

 2NH3 + 3O2 → 2NO2– + 2H+ + 2H2O 

2NO2– + O2 → 2NO3– 

Assimilation 

Plants utilise their roots to absorb nitrogen molecules from the soil. These nitrogen molecules are available in the form of ammonia, nitrite ions, nitrate ions, or ammonium ions and are used in the manufacture of plant and animal proteins. Plants and animals both require nitrogen to make proteins. It is introduced into the food chain in this fashion when the plants are consumed by the main consumers. 

Ammonification 

When living things, such as plants or animals, perish, their nitrogen-containing organic matter is returned to the soil. Decomposers, which may be bacteria or fungus and are often present in the soil, are responsible for converting the organic waste back into ammonium. During the process of breakdown, ammonia is created, which may subsequently be used in a variety of different biological activities. 

Denitrification 

The conversion of nitrate (NO3-) into gaseous nitrogen and the reintroduction of nitrogen compounds into the natural environment are both steps in the denitrification process (N). This is the final stage of the nitrogen cycle, and it takes place without oxygen present. The bacterial species Clostridium and Pseudomonas are responsible for denitrification. This process involves the metabolism of nitrate, which results in the production of oxygen and free nitrogen gas. 

Nitrogen Cycle in Marine Ecosystem 

The nitrogen cycle functions in the exact same manner in marine ecosystems as it does in terrestrial environments. The most notable distinction is that it is caused by bacteria that are native to saltwater environments. 

Nitrogen-containing compounds are released into the water as a byproduct of the sediments’ gradual compression over time, which results in the formation of sedimentary rock. Geological uplift is responsible for the movement of these sedimentary materials toward land. There was a lack of awareness about the significance of these nitrogen-rich sedimentary rocks as a source of nitrogen until very recently. Recent research, on the other hand, has demonstrated that when rocks are weathered, plants benefit from the release of nitrogen into the environment. 

Importance of Nitrogen Cycle 

The importance of the nitrogen cycle may be broken down into many categories, including the following: The importance of the nitrogen cycle may be broken down into many categories, including the following: 

1.Enables plants to produce chlorophyll from nitrogen molecules by acting as a catalyst for the process. 

2.It does this by participating in the metabolic process that transforms inert nitrogen gas into a form that plants can make use of. 

3. During the process of ammonification, the bacteria contribute to the breakdown of plant and animal matter, which assists in the indirect cleaning up of the environment. 

4.Nitrates and nitrites are released into the soil, which helps to replenish the soil with the nutrients that are necessary for agricultural production. 

5.Nitrogen is a fundamental component of every living cell, and it is required for the production of a wide range of vital compounds and proteins. 

Conclusion  

Even though there is a large quantity of nitrogen in the air, plants and animals are unable to make use of it until it is converted into nitrogen molecules. 

Nitrogen-fixing bacteria are microorganisms that convert atmospheric nitrogen into nitrogen compounds that plants are able to use. 

The plant organisms are able to extract usable nitrogen molecules from the soil by means of their root systems. After being taken up by the plant cell, these nitrogen molecules are used in the synthesis of proteins and other compounds. 

Consuming these plants or other animals that contain nitrogen allows organisms to take in nitrogen into their bodies. Proteins are derived from these plants and animals, which are then consumed by humans. After that, the nitrogen is incorporated into our bodies via the process of assimilation. 

Near the conclusion of the nitrogen cycle, when the nitrogenous compounds are absorbed into the soil and consumed by plants once again, the breakdown of organic waste is assisted by bacteria and fungi. 

Microorganisms in the soil are responsible for the ultimate transformation of the nitrogenous compounds in the soil into nitrogen gas. It ultimately returns to the atmosphere. 

Because these cycles continue to repeat endlessly, the quantity of nitrogen that is present in the atmosphere is able to stay stable.