The Nitrogen cycle stands a vital biogeochemical pathway, explaining the flow of nitrogen across the diverse components of Earth's ecosystems. Atmosphere is the reservoir of free gaseous nitrogen and nitrogen compounds are found in the bodies of organisms and in the soil. Living organisms (except some freeliving bacteria) cannot use elemental nitrogen directly. Nitrogen is a crucial element for the formation of proteins and DNA in living organisms and plays a vital role in supporting plant growth and ecosystem productivity. The nitrogen cycle involves several key processes that transform nitrogen into various chemical forms, making it available to different organisms.
There are 5 processes by which the nitrogen moves in the ecosystem in many different forms. The processes are Number 1. Nitrogen fixation, 2. Nitrification, 3. Assimilation, 4. Ammonification and 5. Denitrification.
Nitrogen cycle begins with nitrogen gas in the atmosphere. About 78% of the Earth's atmosphere is molecular nitrogen. But plants cannot use Nitrogen gas directly from the atmosphere. Nitrogen fixation is a natural or industrial process in which the free nitrogen combines chemically with other elements to form nitrogen compounds such as ammonia, nitrates, or nitrites.
Atmospheric nitrogen is fixed in two different ways. Biological and Nonbiological. Biological fixation of nitrogen: In this process, some bacteria convert nitrogen to Ammonia compound or ammonium ions which can be used by plants for food synthesis. Nonbiological fixation: During lightening and some industrial processes, nitrogen is converted to Nitrate, and it dissolve in water which can be utilised by plants for assimilation.
Biological fixations take place by two different types of bacteria: Accordingly, they are again classified as Symbiotic and Nonsymbiotic fixation. Symbiotic fixation: symbiotic means a mutually beneficial relationship. Some bacteria make a symbiotic relationship with the plant roots. Bacteria like Rhizobium has an association with leguminous plants. The bacteria convert nitrogen to Ammonia and is shared with the plant.
Nonsymbiotic fixation: On the other hand, some bacteria like blue green algae, fix the nitrogen independently in the soil.
Rhizobium is a nitrogen fixing microorganism. Rhizobium and leguminous plants have a give and take relationship. Rhizobium establishes a symbiotic relationship with the roots of leguminous plant. The plant roots supply the carbohydrates and protect them within the root noodles. The bacteria produce the ammonia from atmospheric air and store them in the root noodles and share with the plant.
Rhizobia invade the root hairs of host plants, where they multiply and stimulate the formation of root nodules, enlargements of plant cells and bacteria in intimate association. Within the nodules, the bacteria convert free nitrogen to ammonia, which the host plant utilizes for its nourishment. In return the plant supplies the carbohydrates to the bacteria.
Nitrification: Nitrification is the process where ammonium ions are converted into nitrites and then into nitrates by nitrifying bacteria (e.g., Nitrosomonas and Nitrobacter). This conversion makes nitrogen more available to plants, which can absorb nitrates through their roots. First ammonia is oxidized to Nitrite by the species Nitrosomonas. Next Nitrite is further oxidized by Nitrobacter to Nitrate. So, both Nitrosomonas and Nitrobacter are extremely important bacteria for plant nutrition.
Assimilation: Assimilation is associated with digestion and absorption of food or nutrients to incorporate them into its body. Assimilation is how organisms obtain the necessary substances for growth, energy production, and maintaining bodily functions. It's a fundamental part of the nutrition process across the animal and plant kingdoms. Plants absorb nitrates and ammonia from the soil through their roots, and use them to synthesize proteins, nucleic acids, enzymes, etc. Animals assimilate nitrogen by eating the plants and converting them into their own body compounds.
Ammonification: Ammonification is related to decomposition of dead organic matters. When plants and animals die, and when waste products are decomposed by bacteria and fungi, organic nitrogen compounds are broken down into ammonia. This process of breakdown of organic nitrogen compounds is called ammonification This is a very essential link in the food chain of an ecosystem. This releases nitrogen back into the soil.
Denitrification: This is the last step of nitrogen cycle. This process brings the nitrogen back to the atmosphere. Denitrification is a reduction process. A reduction is This biological reduction takes place in an environment of absence of oxygen. The nitrates or nitrites are reduced into gaseous molecular nitrogen by some anaerobic bacteria. It involves stepwise reduction of nitrate to nitrite, to nitric oxide, to nitrous oxide, and finally, to atmospheric dinitrogen