2. Nitrogen Cycle

3. Sources Lightning Inorganic fertilizers Nitrogen Fixation Animal Residues Crop residues Organic fertilizers

5. Forms of Nitrogen Urea  CO(NH 2 ) 2 Ammonia  NH 3 (gaseous) Ammonium  NH 4 Nitrate  NO 3 Nitrite  NO 2 Atmospheric Dinitrogen  N 2 Organic N

6. Global Nitrogen Reservoirs Nitrogen Reservoir Metric tons nitrogen Actively cycled Atmosphere3.9*10 15 No Ocean  soluble salts Biomass 6.9*10 11 5.2*10 8 Yes Land  organic matter  Biota 1.1*10 11 2.5*10 10 Slow Yes

7. Roles of Nitrogen Plants and bacteria use nitrogen in the form of NH 4 + or NO 3 - It serves as an electron acceptor in anaerobic environment Nitrogen is often the most limiting nutrient in soil and water.

8. Nitrogen is a key element for amino acids nucleic acids (purine, pyrimidine) cell wall components of bacteria (NAM).

9. Nitrogen Cycles Ammonification/mineralization Immobilization Nitrogen Fixation Nitrification Denitrification

10. R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N2ON2O N2N2

11. Ammonification or Mineralization R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N2ON2O N2N2

12. Mineralization or Ammonification Decomposers: earthworms, termites, slugs, snails, bacteria, and fungi Uses extracellular enzymes  initiate degradation of plant polymers Microorganisms uses: Proteases, lysozymes, nucleases to degrade nitrogen containing molecules

13. Plants die or bacterial cells lyse  release of organic nitrogen Organic nitrogen is converted to inorganic nitrogen (NH 3 ) When pH<7.5, converted rapidly to NH 4 Example: Urea NH 3 + 2 CO 2

14. Immobilization The opposite of mineralization Happens when nitrogen is limiting in the environment 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

15. Nitrogen Fixation R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N2ON2O N2N2

16. Nitrogen Fixation Energy intensive process : N 2 + 8H+ + 8e - + 16 ATP = 2NH 3 + H 2 + 16ADP + 16 Pi Performed only by selected bacteria and actinomycetes Performed in nitrogen fixing crops (ex: soybeans)

17. Microorganisms fixing Azobacter Beijerinckia Azospirillum Clostridium Cyanobacteria Require the enzyme nitrogenase Inhibited by oxygen Inhibited by ammonia (end product)

18. Rates of Nitrogen Fixation N 2 fixing systemNitrogen Fixation (kg N/hect/year) Rhizobium-legume200-300 Cyanobacteria- moss30-40 Rhizosphere associations 2-25 Free- living1-2

20. Applications to wetlands Occur in overlying waters Aerobic soil Anaerobic soil Oxidized rhizosphere Leaf or stem surfaces of plants

21. Bacterial Fixation Occurs mostly in salt marshes Is absent from low pH peat of northern bogs Cyanobacteria found in waterlogged soils

22. Nitrification R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N2ON2O N2N2

23. Nitrification Two step reactions that occur together : 1 rst step catalyzed by Nitrosomonas 2 NH 4 + + 3 O 2  2 NO 2 - +2 H 2 O+ 4 H + 2 nd step catalyzed by Nitrobacter 2 NO 2 - + O 2  2 NO 3 -

24. Optimal pH is between 6.6-8.0 If pH < 6.0  rate is slowed If pH < 4.5  reaction is inhibited In which type of wetlands do you thing Nitrification occurs?

25. Denitrification R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N2ON2O N2N2

26. Denitrification Removes a limiting nutrient from the environment 4NO 3 - + C 6 H 12 O 6  2N 2 + 6 H 2 0 Inhibited by O 2 Not inhibited by ammonia Microbial reaction Nitrate is the terminal electron acceptor

27. Looking at the Nitrogen cycle through the eye of NH 4

29. Surfac e water Oxidized layer Reduce d soil layer [NH 4 ] HIGH Low [NH 4 ] Slow Diffusion Biodegradati on C/N <20 C/N >20

30. Surfac e water Oxidized layer Reduce d soil layer [NH 4 ] HIGH Low [NH 4 ] Slow Diffusion nitrificatio n [NO 3 ] high

31. Surfac e water Oxidized layer Reduce d soil layer [NO 3 ] high Leaching [NO 3 ] Low N2N2 Denitrificatio n