The Nitrogen CycleThe 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 HydrosphereThe Hydrosphere

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

Hydrosphere Continued…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 LithosphereThe Lithosphere• Rigid outer layer of

earth; Includes crust and upper part of mantle.

• Relatively strong layer in contrast to underlying asthenosphere.

Lithosphere Lithosphere Continued…Continued…

• The brittle most The brittle most upper layer of the upper layer of the Earth that is Earth that is broken up into a broken up into a number of tectonic number of tectonic plates.plates.

• Consists of the Consists of the heavy oceanic and heavy oceanic and lighter continental lighter continental crusts and the crusts and the upper part of the upper part of the mantle.mantle.

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

The Atmosphere• Life on earth is supported by the atmosphere, Life on earth is supported by the atmosphere,

solar energy, and our planet's magnetic fields. solar energy, and our planet's magnetic fields. The atmosphere absorbs the energy from the The atmosphere absorbs the energy from the sun, recycles water and other chemicals, and sun, recycles water and other chemicals, and works with the electrical and magnetic forces to works with the electrical and magnetic forces to provide a moderate climate. provide a moderate climate.

The atmosphereThe atmosphere

• The atmosphere also protects us from high-The atmosphere also protects us from high-energy radiation and the frigid vacuum of energy radiation and the frigid vacuum of space.space.

Composition of AtmosphereComposition of Atmosphere• The atmosphere is The atmosphere is

primarily composed of primarily composed of nitrogen (Nnitrogen (N22, 78%), , 78%), oxygen (Ooxygen (O22, 21%), and , 21%), and argon (Ar, 1%). argon (Ar, 1%).

• A number of other very A number of other very influential components influential components are also present: the are also present: the water (Hwater (H22O, 0 - 7%), O, 0 - 7%), "greenhouse" gases or "greenhouse" gases or ozone (O, 0 - 0.01%), ozone (O, 0 - 0.01%), carbon dioxide (COcarbon dioxide (CO22, , 0.01-0.1%).0.01-0.1%).

continuedcontinued

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

The BiosphereThe Biosphere• The biosphere is the life zone of the Earth and The biosphere is the life zone of the Earth and

includes all living organisms, including man, includes all living organisms, including man, and all organic matter that has not yet and all organic matter that has not yet decomposed. decomposed.

• The biosphere is structured into a hierarchy The biosphere is structured into a hierarchy known as the food chain whereby all life is known as the food chain whereby all life is dependent upon the first tier (i.e. mainly the dependent upon the first tier (i.e. mainly the primary producers that are capable of primary producers that are capable of photosynthesis). photosynthesis).

Biosphere Part 2Biosphere Part 2

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

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

• atmospheric fixation atmospheric fixation by lightning by lightning

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

• industrial fixationindustrial fixation

Atmospheric FixationAtmospheric Fixation

• The enormous energy of The enormous energy of lightning breaks nitrogen lightning breaks nitrogen molecules and enables their molecules and enables their atoms to combine with atoms to combine with oxygen in the air forming oxygen in the air forming nitrogen oxides. nitrogen oxides.

• These dissolve in rain, These dissolve in rain, forming nitrates, that are forming nitrates, that are carried to the earth. carried to the earth.

• Atmospheric nitrogen fixation Atmospheric nitrogen fixation probably contributes some 5-probably contributes some 5-8% of the total nitrogen fixed.8% of the total nitrogen fixed.

Biological FixationBiological Fixation

• The ability to fix nitrogen is found only in The ability to fix nitrogen is found only in certain bacteria.certain bacteria.

• Some live in a symbiotic relationship Some live in a symbiotic relationship with plants of the legume family (e.g., with plants of the legume family (e.g., soybeans, alfalfa). soybeans, alfalfa).

• Some establish symbiotic relationships Some establish symbiotic relationships with plants other than legumes (e.g., with plants other than legumes (e.g., alders).alders).

Continued…Continued…

• Some nitrogen-fixing bacteria live free in Some nitrogen-fixing bacteria live free in the soil. the soil.

• Nitrogen-fixing cyanobacteria are Nitrogen-fixing cyanobacteria are essential to maintaining the fertility of essential to maintaining the fertility of semi-aquatic environments like rice semi-aquatic environments like rice paddies.paddies.

Industrial FixationIndustrial Fixation• Under great pressure, at a temperature Under great pressure, at a temperature

of 600°C, and with the use of a catalyst, of 600°C, and with the use of a catalyst, atmospheric nitrogen and hydrogen atmospheric nitrogen and hydrogen (usually derived from natural gas or (usually derived from natural gas or petroleum) can be combined to form petroleum) can be combined to form ammonia (NH3). ammonia (NH3).

• Ammonia can be used directly as Ammonia can be used directly as fertilizer, but most of its is further fertilizer, but most of its is further processed to urea and ammonium nitrate processed to urea and ammonium nitrate (NH4NO3). (NH4NO3).

DecayDecay

• Proteins made by Proteins made by plants enter and plants enter and pass through food pass through food webs just as webs just as carbohydrates do. carbohydrates do.

• At each trophic level, At each trophic level, their metabolism their metabolism produces organic produces organic nitrogen compounds nitrogen compounds that return to the that return to the environment, chiefly environment, chiefly in excretions. in excretions.

Continued…Continued…

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

NitrificationNitrification• Ammonia can be Ammonia can be

taken up directly taken up directly by plants - usually by plants - usually through their roots. through their roots.

• Most of the Most of the ammonia produced ammonia produced by decay is by decay is converted into converted into nitrates. This is nitrates. This is accomplished in accomplished in two steps: two steps:

• Bacteria of the Bacteria of the genus genus Nitrosomonas Nitrosomonas oxidize NH3 to oxidize NH3 to nitrites(NOnitrites(NO22

-)-). .

• Bacteria of the Bacteria of the genus Nitrobacter genus Nitrobacter oxidize the oxidize the nitrites to nitrites to nitrates (NOnitrates (NO33

--).).

Continued…Continued…

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

AssimilationAssimilation• Plant roots absorb inorganic ammonia, Plant roots absorb inorganic ammonia,

ammonium ions, and nitrate ions. ammonium ions, and nitrate ions. Formed by nitrification and nitrogen Formed by nitrification and nitrogen fixation.fixation.

• Ions are used to make nitrogen Ions are used to make nitrogen containing organic molecules such as:containing organic molecules such as:

– DNADNA

– Amino AcidsAmino Acids

– ProteinsProteins

DentrificationDentrification

• The three processes above remove nitrogen The three processes above remove nitrogen from the atmosphere and pass it through from the atmosphere and pass it through ecosystems.ecosystems.

• Denitrification reduces nitrates to nitrogen gas, Denitrification reduces nitrates to nitrogen gas, thus replenishing the atmosphere. thus replenishing the atmosphere.

• Bacteria are the agents. They live deep in soil Bacteria are the agents. They live deep in soil and in aquatic sediments where conditions are and in aquatic sediments where conditions are anaerobic. They use nitrates as an alternative anaerobic. They use nitrates as an alternative to oxygen for the final electron acceptor in their to oxygen for the final electron acceptor in their respiration. respiration.

Human InfluenceHuman Influence

• German chemist of WWII, Fritz Haber German chemist of WWII, Fritz Haber developed a chemical process in which developed a chemical process in which nitrogen and hydrogen gas combine to nitrogen and hydrogen gas combine to

form gaseous ammonia. form gaseous ammonia.

• Coupled with irrigation, this input of Coupled with irrigation, this input of nitrogen into the soil revolutionized nitrogen into the soil revolutionized agriculture by increasing crop yieldsagriculture by increasing crop yields

Ways Humans Intervene… #1Ways Humans Intervene… #1

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

… #2#2

• We emit heat-trapping nitrous oxide gas into We emit heat-trapping nitrous oxide gas into the atmosphere through anaerobic bacteria on the atmosphere through anaerobic bacteria on

livestock wastes and commercial inorganic livestock wastes and commercial inorganic fertilizers applied to the soilfertilizers applied to the soil

• Emission of this gas rise and account for few Emission of this gas rise and account for few greenhouse gases that can cause global greenhouse gases that can cause global

warmingwarming• When it reaches the stratosphere, it depletes When it reaches the stratosphere, it depletes

some of the ozone layersome of the ozone layer

…3

• We remove nitrogen from the earth's We remove nitrogen from the earth's crust when we mine nitrogen-containing crust when we mine nitrogen-containing

materials for fertilizers materials for fertilizers

• Deplete nitrogen from soil by harvesting Deplete nitrogen from soil by harvesting nitrogen-rich cropsnitrogen-rich crops

• Leach water-soluble nitrate ions from Leach water-soluble nitrate ions from soil by irrigationsoil by irrigation

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

planting cropsplanting crops

…5

• Add excess nitrogen compounds to aqautic Add excess nitrogen compounds to aqautic systems in agricultural runoff, sewage, and systems in agricultural runoff, sewage, and deposition of nitrogen compounds from the deposition of nitrogen compounds from the

atmosphereatmosphere• Stimulates excess growth of algae and other Stimulates excess growth of algae and other

aquatic plantsaquatic plants• Breakdown of dead algae by aerobic Breakdown of dead algae by aerobic

decomposers deplete water of dissolved oxygen decomposers deplete water of dissolved oxygen and disrupt aquatic systems and reduce aquatic and disrupt aquatic systems and reduce aquatic

biodiversitybiodiversity

……66

• Add excess nitrogen compounds to Add excess nitrogen compounds to terrestrial ecosystems through terrestrial ecosystems through

atmospheric deposition…atmospheric deposition…

Atmospheric DepositionAtmospheric Deposition

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

leaves and other surfacesleaves and other surfaces

……6 (continued)6 (continued)

• The nitrogen becomes available for plant The nitrogen becomes available for plant and microbial growth, and can lead to and microbial growth, and can lead to

weeds which can better use nitrogen for weeds which can better use nitrogen for growth, outgrowing/eliminating other growth, outgrowing/eliminating other plants that cant use nitrogen as well.plants that cant use nitrogen as well.

• THUS: our excessive inputs of nitrogen THUS: our excessive inputs of nitrogen into the atmosphere can reduce into the atmosphere can reduce

terrestrial biodiversityterrestrial biodiversity

Works Cited

• 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

Continued…

• 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.