Transcript The Nitrogen Cycle

The Nitrogen Cycle
APES
So… how many planets
will your life take?!
The Nitrogen Cycle
One of the most
important nutrient
cycles found in
terrestrial ecosystems
Movement of various
forms of nitrogen
through the
hydrosphere,
lithosphere and
atmosphere
The Nitrogen Cycle
Composition of Atmosphere
Is primarily
composed of
nitrogen (N2, 78%)
The main abiotic
source of nitrogen in
the cycle
The atmosphere is
considered a major
reservoir of nitrogen
Atmospheric Nitrogen
Nitrogen, mostly in
the form of
ammonium and
nitrate, reaches the
Earth's surface as a
result of
atmospheric
lightning,
precipitation and
industrial pollution.
In the Biosphere
Animals consume nitrogen from plants
Plants consume nitrogen from the soil
Soil gets nitrogen from water or rain
that contains nitrogen.
In the Biosphere
Plants must secure their
nitrogen in "fixed" form
(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 5-8% 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). Ex-Rhizobium bacteria
Some establish symbiotic relationships with
plants other than legumes (e.g., alders).
Legumes and Root Nodules
Biological Fixation
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.
Decay
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-).
Nitrification
These two groups of 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 critical to life such as:
DNA
Proteins
Amino Acids
Dentrification
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 their cellular
respiration reaction.
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
Ways Humans Intervene
#2: We emit heattrapping nitrous
oxide gas into the
atmosphere through
anaerobic bacteria
from livestock
wastes and
commercial
inorganic fertilizers
Ways Humans Intervene
#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
Ways Humans Intervene
#4: Remove nitrogen
from soil when we
burn grasslands and
clear forests before
planting crops
Ways Humans Intervene
#5: Add excess nitrogen compounds to
aquatic 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
Ways Humans Intervene
#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
Ways Humans Intervene
#6, continued: nitrogen
becomes available for
plant and microbial
growth, and can lead to
weeds which can
better use nitrogen for
growth,
outgrowing/eliminatin
g other plants that
can’t use nitrogen as
well
References
http://liftoff.msfc.nasa.gov/academy/space/atmosphere.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/outlines/nitrogencycle.html
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/N/NitrogenCycle.html
http://web.geology.ufl.edu/Biosphere.html
http://www.cas.muohio.edu/~mbi-ws/biogeochemicalcycles/Nitrogen/nitrogen.htm#Ass
http://www.marietta.edu/~biol/102/ecosystem.html#TheNitrogenCycle12
Living in the Environment/Eleventh Edition/G Tyler Miller, Jr.