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).
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