The Nitrogen Cycle

1
The Nitrogen Cycle
2
The Nitrogen Cycle

• Represents one of the most important nutrient
  cycles found in terrestrial ecosystems. Model
  that describes the movement of nitrogen in its
  many forms between the hydrosphere, lithosphere,
  atmosphere, and biosphere.

3
The Hydrosphere

• The hydrosphere describes the waters of the
  earth. Water exists on the earth in various
  stores, including the atmosphere, oceans, lakes,
  rivers, glaciers, snowfields, and groundwater.

4
Hydrosphere Continued

• Water moves from one store to another by way of
  evaporation, condensation, precipitation,
  deposition, runoff, infiltration, sublimation,
  transpiration, and groundwater flow.

5
continued

• The form and movement of nitrogen are greatly
  influenced by components of the hydrologic cycle,
  which is particularly important for agriculture
  and the environment.

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The Lithosphere

• Rigid outer layer of earth Includes crust and
  upper part of mantle.
• Relatively strong layer in contrast to underlying
  asthenosphere.

7
Lithosphere Continued

• The brittle most upper layer of the Earth that is
  broken up into a number of tectonic plates.
• Consists of the heavy oceanic and lighter
  continental crusts and the upper part of the
  mantle.

• The lithosphere rests on a soft layer called the
  asthenosphere, over which the plates of the
  lithosphere glide.

8
The Atmosphere

• Life on earth is supported by the atmosphere,
  solar energy, and our planet's magnetic fields.
  The atmosphere absorbs the energy from the sun,
  recycles water and other chemicals, and works
  with the electrical and magnetic forces to
  provide a moderate climate.
• The atmosphere
• The atmosphere also protects us from high-energy
  radiation and the frigid vacuum of space.

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Composition of Atmosphere

• The atmosphere is primarily composed of nitrogen
  (N2, 78), oxygen (O2, 21), and argon (Ar, 1).
• A number of other very influential components are
  also present the water (H2O, 0 - 7),
  "greenhouse" gases or ozone (O, 0 - 0.01),
  carbon dioxide (CO2, 0.01-0.1).

10
continued

• Nitrogen, mostly in the form of ammonium and
  nitrate, reaches the Earth's surface as a result
  of atmospheric lightning, precipitation and
  industrial pollution.

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The Biosphere

• The biosphere is the life zone of the Earth and
  includes all living organisms, including man, and
  all organic matter that has not yet decomposed.
• The biosphere is structured into a hierarchy
  known as the food chain whereby all life is
  dependent upon the first tier (i.e. mainly the
  primary producers that are capable of
  photosynthesis).

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Biosphere Part 2

• The biosphere can be divided into distinct
  ecosystems that represent the interactions
  between a group of organisms forming a trophic
  pyramid and the environment or habitat in which
  they live.

13
Continued

• Animals consume nitrogen from plants
• Plants consume nitrogen from the soil
• Soil gets nitrogen from water or rain that
  contains nitrogen.

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Nitrogen Cycle Continued

• All life requires nitrogen-compounds, e.G.,
  Proteins and nucleic acids.
• Air, which is 79 nitrogen gas (N2), is the major
  reservoir of nitrogen.
• But most organisms cannot use nitrogen in this
  form.

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• Plants must secure their nitrogen in "fixed"
  form, i.E., Incorporated in compounds such as
  Nitrate ions (NO3-)
• Ammonia (NH3)
• Urea (NH2)2CO
• Animals secure their nitrogen (and all other)
  compounds from plants (or animals that have fed
  on plants).

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Nitrogen Fixation

• Three processes are responsible for most of the
  nitrogen fixation in the biosphere are

• atmospheric fixation by lightning
• biological fixation by certain microbes - alone
  or in a symbiotic relationship with plants
• industrial fixation

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Atmospheric Fixation

• The enormous energy of lightning breaks nitrogen
  molecules and enables their atoms to combine with
  oxygen in the air forming nitrogen oxides.
• These dissolve in rain, forming nitrates, that
  are carried to the earth.
• Atmospheric nitrogen fixation probably
  contributes some 5-8 of the total nitrogen fixed.

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Biological Fixation

• The ability to fix nitrogen is found only in
  certain bacteria.
• Some live in a symbiotic relationship with
  plants of the legume family (e.g., soybeans,
  alfalfa).
• Some establish symbiotic relationships with
  plants other than legumes (e.g., alders).

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Continued

• Some nitrogen-fixing bacteria live free in the
  soil.
• Nitrogen-fixing cyanobacteria are essential to
  maintaining the fertility of semi-aquatic
  environments like rice paddies.

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Industrial Fixation

• Under great pressure, at a temperature of 600C,
  and with the use of a catalyst, atmospheric
  nitrogen and hydrogen (usually derived from
  natural gas or petroleum) can be combined to form
  ammonia (NH3).
• Ammonia can be used directly as fertilizer, but
  most of its is further processed to urea and
  ammonium nitrate (NH4NO3).

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Decay

• Proteins made by plants enter and pass through
  food webs just as carbohydrates do.
• At each trophic level, their metabolism produces
  organic nitrogen compounds that return to the
  environment, chiefly in excretions.

22
Continued

• The final beneficiaries of these materials are
  microorganisms of decay. They break down the
  molecules in excretions and dead organisms into
  ammonia.

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Nitrification

• Ammonia can be taken up directly by plants -
  usually through their roots.
• Most of the ammonia produced by decay is
  converted into nitrates. This is accomplished in
  two steps

• Bacteria of the genus Nitrosomonas oxidize NH3 to
  nitrites(NO2-).
• Bacteria of the genus Nitrobacter oxidize the
  nitrites to nitrates (NO3-).

24
Continued

• These two groups or autotrophic bacteria are
  called nitrifying bacteria. Through their
  activities (which supply them with all their
  energy needs), nitrogen is made available to the
  roots of plants.

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Assimilation

• Plant roots absorb inorganic ammonia, ammonium
  ions, and nitrate ions. Formed by nitrification
  and nitrogen fixation.
• Ions are used to make nitrogen containing organic
  molecules such as
• DNA
• Amino Acids
• Proteins

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Dentrification

• The three processes above remove nitrogen from
  the atmosphere and pass it through ecosystems.
• Denitrification reduces nitrates to nitrogen gas,
  thus replenishing the atmosphere.
• Bacteria are the agents. They live deep in soil
  and in aquatic sediments where conditions are
  anaerobic. They use nitrates as an alternative to
  oxygen for the final electron acceptor in their
  respiration.

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Human Influence

• German chemist of WWII, Fritz Haber developed a
  chemical process in which nitrogen and hydrogen
  gas combine to form gaseous ammonia.
• Coupled with irrigation, this input of nitrogen
  into the soil revolutionized agriculture by
  increasing crop yields

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Ways Humans Intervene 1

• We emit a large amount of nitrogen into the
  atmosphere when we burn fuel

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2

• We emit heat-trapping nitrous oxide gas into the
  atmosphere through anaerobic bacteria on
  livestock wastes and commercial inorganic
  fertilizers applied to the soil
• Emission of this gas rise and account for few
  greenhouse gases that can cause global warming
• When it reaches the stratosphere, it depletes
  some of the ozone layer

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3

• We remove nitrogen from the earth's crust when we
  mine nitrogen-containing materials for
  fertilizers
• Deplete nitrogen from soil by harvesting
  nitrogen-rich crops
• Leach water-soluble nitrate ions from soil by
  irrigation

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4

• Remove nitrogen from soil when we burn grasslands
  and clear forests before planting crops

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5

• Add excess nitrogen compounds to aqautic systems
  in agricultural runoff, sewage, and deposition of
  nitrogen compounds from the atmosphere
• Stimulates excess growth of algae and other
  aquatic plants
• Breakdown of dead algae by aerobic decomposers
  deplete water of dissolved oxygen and disrupt
  aquatic systems and reduce aquatic biodiversity

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6

• Add excess nitrogen compounds to terrestrial
  ecosystems through atmospheric deposition

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Atmospheric Deposition

• The movement of reactive nitrogen compounds, such
  as nitric acid, nitrogen dioxide, from the
  atmosphere onto plant leaves and other surfaces

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6 (continued)

• The nitrogen becomes available for plant and
  microbial growth, and can lead to weeds which can
  better use nitrogen for growth,
  outgrowing/eliminating other plants that cant use
  nitrogen as well.
• THUS our excessive inputs of nitrogen into the
  atmosphere can reduce terrestrial biodiversity

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Works Cited

• http//liftoff.msfc.nasa.gov/academy/space/atmosph
  ere.html
• http//www.geog.ouc.bc.ca/physgeog/contents/images
  /lithosphere.gif
• http//www.oilandgas.org.uk/issues/images/z0002409
  .gif

• http//www.webref.org/geology/1/lithosphere.htm
• http//www.bartleby.com/65/li/lithosph.html
• http//www.elmhurst.edu/chm/onlcourse/chm110/outl
  ines/nitrogencycle.html
• http//users.rcn.com/jkimball.ma.ultranet/BiologyP
  ages/N/NitrogenCycle.html

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Continued

• http//web.geology.ufl.edu/Biosphere.html
• http//www.cas.muohio.edu/mbi-ws/biogeochemicalcy
  cles/Nitrogen/nitrogen.htmAss

• http//www.marietta.edu/biol/102/ecosystem.htmlT
  heNitrogenCycle12
• Living in the Environment/Eleventh Edition/G
  Tyler Miller, Jr.