Nitrogen cycle is called a perfect cycle in the biosphere because it keeps or maintains the over all amount of nitrogen constant in atmosphere, soil and water.
Nitrogen cycle depends upon at least four different kinds of bacteria known as the decay causers, the nitrifiers, the denitrifiers, and the nitrogen fixers. There is a regular circulation of nitrogen through the air, soil, plants and animals through nitrogen cycle.
Different stages of nitrogen cycle:
- Some nitrogen fixing bacteria such as Azotobactor and Rhizobium convert the atmospheric nitrogen into nitrates which are soluble in water. This process is known as nitrogen fixation.
- During lightining nitrogen of atmosphere reacts with oxygen and ultimately form dilute nitric acid. This acid comes down to earth with rainwater.
- Nitrates are absorbed by plants into their system and utilized for making organic matter like protein etc.
- When animals consume plant matter, the break down the plant 's nitrogenous compounds and use them to form new animal proteins and other cell components.
- After an animal excretes urea or uric acid or after an animal or plant dies, certain bacteria carry out ammonification, that is they produce ammonium ions from nitrogen-containing molecules.
- Plants can then assimilate this ammonium ion or other bacteria can change it to nitrate by nitrification. Plants can take in some of the nitrates produced in this way.
- Some microorganisms convert ammonia into nitrates. This process is know as nitrification.
- There are some other bacteria which reduce nitrates back to nitrogen or to ammonia or to some other oxides. This process is known as denitrification.
- Free nitrogen returns back to atmosphere and oxides are taken up by plants.
Nitrogen Cycle Diagram - I
Organisms invovled in Nitrogen cycle:
Name of Microorganisms | Role played in Nitrogen Cycle |
Rhizobium bacteria ( in root nodules) | Nitrogen Fixation |
Azotobactor bacteria ( in soil) | Nitrogen Fixation ( converts atmospheric nitrogen gas into nitrogen compounds) |
Blue green algae | Nitrogen Fixation |
Putrefying bacteria | Ammonification |
Fungi | Ammonification ( converts nitrogen containing proteins of dead plants and animals into ammonia |
Nitrifying bacteria | Nitrification ( converts ammonia into nitrites and then into nitrates) |
Nitrosomonas bacteria | Converts ammonia into nitrites |
Nitrobacter bacteria | Converts nitrites into nitrates |
Denitrifying bacteria ( Pseudomonas) | Denitrification ( converts nitrate salts into free nitrogen gas |
Nitrogen Cycle Diagram - Ii
Nitrogen cycle diagram:
