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.
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
1) Nitrogen fixation
2) Ammonification
3) Assimilation
4) Nitrification
5) Denitrification
14.
15. 1)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
16. 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.
17. 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
Deaminas
e
Alanine Pyruvic
acid
Ammoni
a
18. 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.
which converts ammonia to nitrites.
• Other bacterial species such as Nitrobacter are
responsible for the oxidation of the nitrities to nitrates.
• Ammonia gas is toxic to plants.
a) 2NH3 + 1/2O2 NO2 + 2H + H20
b) NO2 + 1/2O2 NO3
Ammoni
a
Nitrite
Nitrite Nitrate
20. 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
23. Role of microbes in nitrogen cycle
1) Nitrogen fixation through symbiotic relationship.
2) Bacteria break down proteins through the
process by decay.
3) Nitrosomonas and Nitrobacter help in
nitrification.
4) Anamox, Pseudomonas or clostridia help in
denitrification.
