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NITROGEN CYCLE
Nitro gen Cycle
• Composes about four-fifths (78.03 percent) by
volume of the atmosphere
• an essential part of the amino acids. It is a basic
element of life.
• is an important element in plant nutrition
• in the form of protein is an important constituent
of animal tissue.
Nitrogen Cycle
•
natural cyclic process in the course of which
atmospheric nitrogen enters the soil and
becomes part of living organisms
Nitrogen Cycle
Amounts of Nitrogen
Nitrogen Reservoir
Metric tons nitrogen
Atmosphere
3.9*1015
Land  organic matter
 Biota
1.1*1011
2.5*1010
Ocean  soluble salts
Biomass
6.9*1011
5.2*108
Forms of Nitrogen in Ocean
Form
Formula
Function
Pathway
Habitat
Nitrate
NO3 _
Electron acceptor,
nitrogen source
Nitrogen assimilation,
dissimilatory nitrate
reduction and
denitrification
Coastal upwelling zones, deep
ocean
Ammonium
NH4+
Electron donor, energy
source, nitrogen source
Nitrogen assimilation,
ammonia oxidation
(aerobic), and anaerobic
ammonia oxidation
Important, rapidly recycled pool in
open ocean, intermediate in
decomposition of organic matter
Electron donor and
acceptor, energy source,
nitrogen source
Nitrification (nitrite
oxidation), denitrification
Found at margins of oxic/anoxic
regions, intermediate in oxidation
and reduction pathways
_______
High concentration in equilibrium
with atmosphere, available to
N2-fixing microorganisms
Nitrite
NO2
-
Dinitrogen
N2
Nitrogen source
Nitrous oxide
N 2O
Trace gas, electron
acceptor, electron donor
End or by-product of
nitrification and
denitrification
Intermediate in reductive pathway,
also formed in nitrification and at
oxic/anoxic interfaces and anoxic
or suboxic zones
Urea
CH4N2O
Nitrogen source
Nitrogen assimilation
Decomposition product,
potentially important nitrogen
source in water column
Steps of Nitrogen Cycle
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•
•
•
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Nitrogen Fixation
Nitrogen Assimilation
Ammonification
Nitrification
Denitrification
Nitrogen Fixation
• Nitrogen gas is converted into
inorganic nitrogen compounds. It is mostly
(90 percent) accomplished by free-living,
nitrogen-fixing bacteria.
Nitrogen-Fixing Bacteria
• symbiotic bacteria living on the roots of
plants (mostly legumes and alders)
• cyanobacteria (formerly known as bluegreen algae)
• archaebacteria (also known as archaea)
in deep-sea hydrothermal vents
Nitrogen Fixation by Lightning
• The high energies provided by lightning
and cosmic radiation serve to combine
atmospheric nitrogen and oxygen into
nitrates, which are carried to the Earth’s
surface in precipitation.
Steps of Nitrogen Cycle
•
•
•
•
•
Nitrogen Fixation
Nitrogen Assimilation
Ammonification
Nitrification
Denitrification
Nitrogen Assimilation
• are assimilation of nitrates and ammonia
resulting from nitrogen fixation into the
specific tissue compounds of algae and
higher plants. Animals then ingest these
algae and plants, converting them into their
own body compounds.
Steps of Nitrogen Cycle
•
•
•
•
•
Nitrogen Fixation
Nitrogen Assimilation
Ammonification
Nitrification
Denitrification
Ammonification
• The remains of all living things—and their
waste products—are decomposed by
microorganisms which yields ammonia.
Steps of Nitrogen Cycle
•
•
•
•
•
Nitrogen Fixation
Nitrogen Assimilation
Ammonification
Nitrification
Denitrification
Nitrification
• a process carried out by nitrifying
bacteria, transforms soil ammonia into
nitrates, which plants can incorporate into
their own tissues.
1rst step catalyzed
by Nitrosomonas
2 NH4+ + 3 O2  2
NO2- +2 H2O+ 4 H+
2nd step catalyzed
by Nitrobacter
2 NO2- + O2  2
NO3-
Steps of Nitrogen Cycle
•
•
•
•
•
Nitrogen Fixation
Nitrogen Assimilation
Ammonification
Nitrification
Denitrification
Denitrification
• The process where nitrates are
metabolized by denitrifying bacteria to
free nitrogen and returned to the
atmosphere
Nitrogen Cycle in Ocean
• In groups construct a poster or drawing
diagram about how the Nitrogen Cycle
would work in the ocean
• Label steps (Nitrogen Fixation, Nitrogen Assimilation, Ammonification,
Nitrification, Denitrification)
Nitrogen Cycle In Ocean
Nitrogen Cycle in Fish Tanks