Nitrogen cycle
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Nitrogen cycle






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Nitrogen cycle Nitrogen cycle Presentation Transcript

  • Nitrogen Cycle
  • Sources• Lightning• Inorganic fertilizers• Nitrogen Fixation• Animal Residues• Crop residues• Organic fertilizers
  • Forms of Nitrogen• Urea  CO(NH2)2• Ammonia  NH3 (gaseous)• Ammonium  NH4• Nitrate  NO3• Nitrite  NO2• Atmospheric Dinitrogen N2• Organic N
  • Global Nitrogen ReservoirsNitrogenReservoirMetric tonsnitrogenActively cycledAtmosphere 3.9*1015NoOcean  solublesaltsBiomass6.9*10115.2*108YesYesLand  organicmatter Biota1.1*10112.5*1010SlowYes
  • Roles of Nitrogen• Plants and bacteria use nitrogen in theform of NH4+or NO3-• It serves as an electron acceptor inanaerobic environment• Nitrogen is often the most limitingnutrient in soil and water.
  • Nitrogen is a key element for• amino acids• nucleic acids (purine, pyrimidine)• cell wall components of bacteria (NAM).
  • Nitrogen Cycles• Ammonification/mineralization• Immobilization• Nitrogen Fixation• Nitrification• Denitrification
  • Ammonification or MineralizationR-NH2NH4 NO2NO3NO2NON2ON2
  • Mineralization or Ammonification• Decomposers: earthworms, termites, slugs,snails, bacteria, and fungi• Uses extracellular enzymes  initiatedegradation of plant polymers• Microorganisms uses:• Proteases, lysozymes, nucleases to degradenitrogen containing molecules
  • • Plants die or bacterial cells lyse  release oforganic nitrogen• Organic nitrogen is converted to inorganicnitrogen (NH3)• When pH<7.5, converted rapidly to NH4• Example:Urea NH3 + 2 CO2
  • Immobilization• The opposite of mineralization• Happens when nitrogen is limiting in theenvironment• Nitrogen limitation is governed by C/N ratio• C/N typical for soil microbial biomass is 20• C/N < 20 Mineralization• C/N > 20 Immobilization
  • Nitrogen FixationR-NH2NH4 NO2NO3NO2NON2ON2
  • Nitrogen Fixation• Energy intensive process :• N2+ 8H+ + 8e-+ 16 ATP= 2NH3+ H2+ 16ADP+ 16 Pi• Performed only by selected bacteria andactinomycetes• Performed in nitrogen fixing crops(ex: soybeans)
  • Microorganisms fixing• Azo bacte r• Be ije rinckia• Azo spirillum• Clo stridium• Cyano bacte ria• Require the enzymenitrogenase• Inhibited by oxygen• Inhibited byammonia (endproduct)
  • Rates of Nitrogen FixationN2 fixing system Nitrogen Fixation (kgN/hect/year)Rhizobium-legume 200-300Cyanobacteria- moss 30-40Rhizosphereassociations2-25Free- living 1-2
  • Applications to wetlands• Occur in overlying waters• Aerobic soil• Anaerobic soil• Oxidized rhizosphere• Leaf or stem surfaces of plants
  • Bacterial Fixation• Occurs mostly in salt marshes• Is absent from low pH peat of northernbogs• Cyanobacteria found in waterloggedsoils
  • NitrificationR-NH2NH4 NO2NO3NO2NON2ON2
  • NitrificationTwo step reactions that occur together :• 1rststep catalyzed by Nitro so m o nas2 NH4++ 3 O2  2 NO2-+2 H2O+ 4 H+• 2ndstep catalyzed by Nitro bacte r• 2 NO2-+ O2  2 NO3-
  • • Optimal pH is between 6.6-8.0• If pH < 6.0  rate is slowed• If pH < 4.5  reaction is inhibitedIn which type of wetlands doyou thing Nitrification occurs?
  • DenitrificationR-NH2NH4 NO2NO3NO2NON2ON2
  • Denitrification• Removes a limiting nutrient from theenvironment• 4NO3-+ C6H12O6 2N2 + 6 H20• Inhibited by O2• Not inhibited by ammonia• Microbial reaction• Nitrate is the terminal electron acceptor
  • Looking at the Nitrogen cyclethrough the eye of NH4
  • Surface waterOxidizedlayerReducedsoillayer[NH4]HIGHLow[NH4]Slow DiffusionBiodegradationC/N <20C/N >20
  • Surface waterOxidizedlayerReducedsoillayer[NH4]HIGHLow[NH4]Slow Diffusionnitrification[NO3] high
  • Surface waterOxidizedlayerReducedsoillayer[NO3] highLeaching[NO3] LowN2Denitrification