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Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
Nitrogen cycle
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Nitrogen cycle

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  • 1. Nitrogen Cycle
  • 2. Sources• Lightning• Inorganic fertilizers• Nitrogen Fixation• Animal Residues• Crop residues• Organic fertilizers
  • 3. Forms of Nitrogen• Urea  CO(NH2)2• Ammonia  NH3 (gaseous)• Ammonium  NH4• Nitrate  NO3• Nitrite  NO2• Atmospheric Dinitrogen N2• Organic N
  • 4. Global Nitrogen ReservoirsNitrogenReservoirMetric tonsnitrogenActively cycledAtmosphere 3.9*1015NoOcean  solublesaltsBiomass6.9*10115.2*108YesYesLand  organicmatter Biota1.1*10112.5*1010SlowYes
  • 5. 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.
  • 6. Nitrogen is a key element for• amino acids• nucleic acids (purine, pyrimidine)• cell wall components of bacteria (NAM).
  • 7. Nitrogen Cycles• Ammonification/mineralization• Immobilization• Nitrogen Fixation• Nitrification• Denitrification
  • 8. R-NH2NH4 NO2NO3NO2NON2ON2
  • 9. Ammonification or MineralizationR-NH2NH4 NO2NO3NO2NON2ON2
  • 10. 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
  • 11. • 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
  • 12. 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
  • 13. Nitrogen FixationR-NH2NH4 NO2NO3NO2NON2ON2
  • 14. 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)
  • 15. Microorganisms fixing• Azo bacte r• Be ije rinckia• Azo spirillum• Clo stridium• Cyano bacte ria• Require the enzymenitrogenase• Inhibited by oxygen• Inhibited byammonia (endproduct)
  • 16. Rates of Nitrogen FixationN2 fixing system Nitrogen Fixation (kgN/hect/year)Rhizobium-legume 200-300Cyanobacteria- moss 30-40Rhizosphereassociations2-25Free- living 1-2
  • 17. Applications to wetlands• Occur in overlying waters• Aerobic soil• Anaerobic soil• Oxidized rhizosphere• Leaf or stem surfaces of plants
  • 18. Bacterial Fixation• Occurs mostly in salt marshes• Is absent from low pH peat of northernbogs• Cyanobacteria found in waterloggedsoils
  • 19. NitrificationR-NH2NH4 NO2NO3NO2NON2ON2
  • 20. 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-
  • 21. • 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?
  • 22. DenitrificationR-NH2NH4 NO2NO3NO2NON2ON2
  • 23. 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
  • 24. Looking at the Nitrogen cyclethrough the eye of NH4
  • 25. Surface waterOxidizedlayerReducedsoillayer[NH4]HIGHLow[NH4]Slow DiffusionBiodegradationC/N <20C/N >20
  • 26. Surface waterOxidizedlayerReducedsoillayer[NH4]HIGHLow[NH4]Slow Diffusionnitrification[NO3] high
  • 27. Surface waterOxidizedlayerReducedsoillayer[NO3] highLeaching[NO3] LowN2Denitrification

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