Transcript The Nitrogen Cycle

The Nitrogen Cycle
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.
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.
Hydrosphere Continued…
• Water moves from one
store to another by
way of: evaporation,
condensation,
precipitation,
deposition, runoff,
infiltration,
sublimation,
transpiration, and
groundwater flow.
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.
The Lithosphere
• Rigid outer layer of
earth; Includes crust
and upper part of
mantle.
• Relatively strong
layer in contrast to
underlying
asthenosphere.
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.
• 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
• The atmosphere also protects us from highenergy radiation and the frigid vacuum of
space.
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, 0.010.1%).
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.
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).
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.
Continued…
• Animals consume nitrogen from plants
• Plants consume nitrogen from the soil
• Soil gets nitrogen from water or rain that
contains nitrogen.
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.
• 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).
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
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 58% of the total nitrogen fixed.
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).
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.
Industrial Fixation
• Under great pressure, at a temperature of
600°C, 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).
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.
Continued…
• The final beneficiaries of these
materials are microorganisms of
decay. They break down the
molecules in excretions and dead
organisms into ammonia.
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-).
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.
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
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.
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
Ways Humans Intervene… #1
• We emit a large amount of nitrogen into the
atmosphere when we burn fuel
… #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
…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
…4
• Remove nitrogen from soil when we burn
grasslands and clear forests before
planting crops
…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
…6
• Add excess nitrogen compounds to
terrestrial ecosystems through
atmospheric deposition…
Atmospheric Deposition
• The movement of reactive nitrogen
compounds, such as nitric acid, nitrogen
dioxide, from the atmosphere onto plant
leaves and other surfaces
…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
Works Cited
• http://liftoff.msfc.nasa.
gov/academy/space/at
mosphere.html
• http://www.geog.ouc.b
c.ca/physgeog/content
s/images/lithosphere.gi
f
• http://www.oilandgas.
org.uk/issues/images/z
0002409.gif
• http://www.webref.org/ge
ology/1/lithosphere.htm
• http://www.bartleby.com/6
5/li/lithosph.html
• http://www.elmhurst.edu/~
chm/onlcourse/chm110/ou
tlines/nitrogencycle.html
• http://users.rcn.com/jkimb
all.ma.ultranet/BiologyPag
es/N/NitrogenCycle.html
Continued…
• http://web.geology.ufl.
edu/Biosphere.html
• http://www.cas.muohi
o.edu/~mbiws/biogeochemicalcyc
les/Nitrogen/nitrogen.
htm#Ass
• http://www.marietta.ed
u/~biol/102/ecosystem
.html#TheNitrogenCy
cle12
• Living in the
Environment/Eleventh
Edition/G Tyler Miller,
Jr.