NITROGEN%20CYCLE

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NITROGEN CYCLE

• Submitted by,
• SREEJITH P
• S4 EEE
• ROLL NO- 54

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CONTENTS

• Introduction
• Processes of the nitrogen cycle
• Human influences on the nitrogen cycle
• References

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INTRODUCTION

• Earth's atmosphere is about 78 nitrogen.
• Nitrogen is essential for many biological
  processes and is crucial for any life on Earth.
• It is in all amino acids, is incorporated into
  proteins, and is present in the bases that make
  up nucleic acids, such as DNA and RNA.

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Nitrogen cycle

• The nitrogen cycle is the biogeochemical cycle
  that describes the transformations of nitrogen
  and nitrogen-containing compounds in nature.
• It is a gaseous cycle.

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Processes of the nitrogen cycle

• Conversion of N2
• Assimilation
• Ammonification
• Nitrification
• Denitrification
• Anaerobic ammonium oxidation

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CONVERSION OF N2

• The conversion of nitrogen (N2) from the
  atmosphere into a form readily available to
  plants and hence to animals and humans is an
  important step in the nitrogen cycle, that
  determines the supply of this essential nutrient.
  
• There are four ways to convert N2 (atmospheric
  nitrogen gas) into more chemically reactive
  forms
• 1.Biological fixation
• 2.Industrial N-fixation
• 3.Combustion of fossil fuels 
• 4.Other processes

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• 1. Biological fixation some symbiotic bacteria
  (most often associated with leguminous plants)
  and some free-living bacteria are able to fix
  nitrogen and assimilate it as organic nitrogen.
  An example of nitrogen fixing bacteria is the
  Rhizobium bacteria, which live in legume root
  nodules. An example of the free-living bacteria
  is Azotobacter.
• 2.Industrial N-fixation  in the Haber-Bosch
  process, N2 is converted together with hydrogen
  gas (H2) into ammonia (NH3) which is used to make
  fertilizer and explosives.

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• 3.Combustion of fossil fuels  automobile engines
  and thermal power plants, which release various
  nitrogen oxides (NOx).
• 4.Other processes  Additionally, the formation
  of NO from N2 and O2 due to photons and
  especially lightning, are important for
  atmospheric chemistry, but not for terrestrial or
  aquatic nitrogen turnover.

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Assimilation

• Plants can absorb nitrate or ammonium ions from
  the soil via their root hairs.
• If nitrate is absorbed, it is first reduced to
  nitrite ions and then ammonium ions for
  incorporation into amino acids, nucleic acids,
  and chlorophyll.
• In plants which have a mutualistic relationship
  with rhizobia, some nitrogen is assimilated in
  the form of ammonium ions directly from the
  nodules.
• Animals, fungi, and other heterotrophic organisms
  absorb nitrogen as amino acids, nucleotides and
  other small organic molecules.

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Ammonification

• When a plant or animal dies, or an animal
  excretes, the initial form of nitrogen is
  organic.
• Bacteria, or in some cases, fungi, converts the
  organic nitrogen within the remains back into
  ammonia, a process called ammonification or
  mineralization.

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Nitrification

• The conversion of ammonia to nitrates is
  performed primarily by soil-living bacteria and
  other nitrifying bacteria.
• The primary stage of nitrification, the oxidation
  of ammonia (NH3) is performed by bacteria such as
  the Nitrosomonas species, which converts ammonia
  to nitrites (NO2-).
• Other bacterial species, such as the
  Nitrobacter, are responsible for the oxidation of
  the nitrites into nitrates (NO3-).

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Denitrification

• Denitrification is the reduction of nitrites back
  into the largely inert nitrogen gas (N2),
  completing the nitrogen cycle.
• This process is performed by bacterial species
  such as Pseudomonas and Clostridium in anaerobic
  conditions.
• They use the nitrate as an electron acceptor in
  the place of oxygen during respiration.
• These facultatively anaerobic bacteria can also
  live in aerobic conditions.

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Anaerobic ammonium oxidation

• In this biological process, nitrite and ammonium
  are converted directly into dinitrogen gas.
• This process makes up a major proportion of
  dinitrogen conversion in the oceans.

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SCHEMATIC REPRESENTATION OF THE FLOW OF NITROGEN
THROUGH THE ENVIRONMENT.
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Human influences on the nitrogen cycle

• As a result of extensive cultivation of legumes
  (particularly soy, alfalfa, and clover), growing
  use of the Haber-Bosch process in the creation of
  chemical fertilizers, and pollution emitted by
  vehicles and industrial plants, human beings have
  more than doubled the annual transfer of nitrogen
  into biologically available forms.
• In addition, humans have significantly
  contributed to the transfer of nitrogen trace
  gases from Earth to the atmosphere, and from the
  land to aquatic systems.
• N2O has risen in the atmosphere as a result of
  agricultural fertilization, biomass burning,
  cattle and feedlots, and other industrial sources.

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• N2O has deleterious effects in the stratosphere,
  where it breaks down and acts as a catalyst in
  the destruction of atmospheric ozone.
• Ammonia (NH3) in the atmosphere has tripled as
  the result of human activities.
• It is a reactant in the atmosphere, where it acts
  as an aerosol, decreasing air quality and
  clinging on to water droplets, eventually
  resulting in acid rain.
• Fossil fuel combustion has contributed to a 6 or
  7 fold increase in NOx flux to the atmosphere.

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• NOx actively alters atmospheric chemistry, and is
  a precursor of tropospheric (lower atmosphere)
  ozone production, which contributes to smog, acid
  rain, and increases nitrogen inputs to
  ecosystems.
• Ecosystem processes can increase with nitrogen
  fertilization, but anthropogenic input can also
  result in nitrogen saturation, which weakens
  productivity and can kill plants.
• Decreases in biodiversity can also result if
  higher nitrogen availability increases
  nitrogen-demanding grasses, causing a degradation
  of nitrogen-poor, species diverse heathlands.

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Reference

• http//en.wikipedia.org/wiki/nitrogen cycle
• http//www.ucsusa.org/clean_energy/nitrogenbasics/
  
• http//www.aquariumdomain.com/guideTheNitrogenCycl
  e.asp

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