Nitrogen cycle

The biogeochemical nitrogen cycle

1. A Seminar On Nitrogen Cycle Presented By Manisha Thakur

2. Biogeochemical cycle In geography and Earth science, a biogeochemical cycle or cycling of a substance is a pathway by which a chemical substance moves through biotic (biosphere) and abiotic (lithosphere, atmosphere and hydrosphere)compartments of Earth. There are biogeochemical cycles for nitrogen, carbon, phosphorous, sulfur, oxygen and water.

3. BIOGEOCHEMICAL CYCLES WATER CYCLE

4. NITROGEN CYCLE

5. Introduction Nitrogen is found to have either 3 or 5 valence electron. Lies at the top of group 15 on periodic table. Molecular nitrogen is not reactive at standard temperature and pressure. Nitrogen is a non-metal, colorless, odorless. Largest source of nitrogen is in the atmosphere. Nitrogen makes up 78% of our air ! Nitrogen is an essential component. Discovered by Scottish physician Daniel Rutherford in 1772.

6. Physical properties It is considered as inert gas. Melting point is -210C Boiling point -195.8C It has the solubilizing property, and less soluble in water. Chemical properties Color of indicator is not affected by nitrogen. Nitrogen can combine with other elements and form different compounds. Nitrogen is a non flammable compound. Nitrogen combines with certain metals to form active metals such as lithium and magnesium. After ionization the energy of nitrogen is given as 1402kJ/mol.

7. Source and distribution Largest source of nitrogen is present in atmosphere. Nitrogen gas comprises 78% of the volume of Earth’s air. Appears in 0.002% OF Earth’s crust by mass. Compounds of nitrogen are found in foods, explosives, poisons and fertilizers. It is one of the largest industrial gases, and is produced commercially as a gas and a liquid. Nitrogen makes up DNA in the form of nitrogenous bases. Nitrogen is distributed from air to soil and environment.

8. Forms of nitrogen It is in the form of dinitrogen (N2) gas. In addition to dinitrogen other organic and inorganic forms exist. Organic form of nitrogen make up a very high percentage of the total nitrogen. Plants are able to use only very specific inorganic forms of nitrogen. It is present in the form of organic nitrogen, ammonia, ammonium, nitrite, nitrate, nitrous oxide, nitric oxide or inorganic nitrogen

9. Nitrogen fixation The process by which inorganic molecular nitrogen(N2) from the atmosphere is incorporated first into ammonia and then into organic compounds that are of use to organism. Nitrogenase enzyme plays a very important role. Nitrogen fixing bacteria are involved. Types of nitrogen fixation Symbiotic nitrogen Non-symbiotic nitrogen fixation

10. Symbiotic fixation Nitrogen reduction by symbiotic microbes. The diazotrophs derive nourishment from plant root and provide nitrogen to it. These process to form nodule development. Eg : Rhizobium , Frankia etc.

11. Non symbiotic nitrogen fixation Some microorganisms live independently in the soil and do nitrogen fixation. Nitrogen fixation by these microbes is called non-symbiotic nitrogen fixation. Of the 175*10^6 tones of total global nitrogen fixation, 190*10^6 tones is contributed by non-symbiotic fixers. Non- symbiotic nitrogen fixers are divided into two groups Free living autotrophic diazotrophs : synthesize own food by photosynthesis using sunlight or chemicals Eg : Clyndrospermum , Plectonema , Tolupotrix . Free living heterotrophic diazotrophs : Use organic matter as food and do nitrogen fixation. Eg : Clostridium, Azotobacter , Klebsiella , Beijrinckia

12. NITROGEN CYCLE The nitrogen cycle is a biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among the atmosphere, terrestrial and marine environment . This conversion can be done by both physical and biological methods . It is of particular interest to Ecologists. Nitrogen availability can effect rate of key ecosystem process, including primary production and decomposition. Alteration in global nitrogen cycle has been observed. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers and release of nitrogen in waste water.

13. Important processes in the nitrogen cycle include Nitrogen fixation Ammonification Assimilation Nitrification Denitrification

14. Nitrogen fixation : Conversion of nitrogen to nitrates and nitrites through atmosphere, industrial and biological process is called as nitrogen fixation. Between 5*10^12and 10*101^2gm/year nitrogen is fixed by lightning strikes. But most fixation is done by free-living or symbiotic bacteria known as Diazotrophs . These bacteria have the nitrogenase enzyme . N2 2NH3 H3 Nitrogen Ammonia

15. 2 ) Assimilation It is the incorporation of inorganic nitrogen compounds into organic molecules. Nitrates and ammonia resulting from nitrogen fixation are assimilated or incorporated into the specific tissue. In plants that have a symbiotic relationship with rhizobia , nitrogen is assimilated in the form of ammonium ions directly from roots .

16. 3 ) Ammonification The remains of all living thing and their waste products are decomposed by microorganisms in the process of ammonification which yields ammonia from organic nitrogen. Ammonia can leave the soil or be converted into other nitrogen compounds depending on part of soil condition. CH3CHNH2COOH+1/2O2 CH3COCOOH+NH3 Alanine Deaminase Alanine Pyruvic acid Ammonia

17. 4) Nitrification The conversion of ammonium to nitrate is performed mainly by the Nitrifying bacteria . In the primary stage of nitrification, the oxidation of ammonium to nitrate is performed by Nitrosomonas sps . w hich converts ammonia to nitrites. Other bacterial species such as Nitrobacter are responsible for the oxidation of the nitrities to nitrates. A mmonia gas is toxic to plants. 2NH3 + 1/2O2 NO2 + 2H + H20 b) NO2 + 1/2O2 NO3 Ammonia Nitrite Nitrite Nitrate

18. 3 2 3 Nitrification

19. 5) Denitrification Denitrification is the reduction of nitrates back into nitrogen gas (N2), completing the nitrogen cycle. This process is performed by bacterial species such as Pseudomonas and Clostridium in anaerobic conditions. They use the nitrate as an electron acceptor in the place of oxygen during respiration. Denitrification occurs in anaerobic conditions . NH4 NO2 NO3 NO2 N2

20. Dinitrification

21. Chemical reactions involved in Nitrogen cycle.

22. Role of microbes in nitrogen cycle Nitrogen fixation through symbiotic relationship. Bacteria break down proteins through the process by decay. Nitrosomonas and Nitrobacter help in nitrification. Anamox , Pseudomonas or clostridia help in denitrification .

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