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.
Nitrogen is a key element for amino acids nucleic acids (purine, pyrimidine) cell wall components of bacteria (NAM).
Ammonification or Mineralization R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N2ON2O N2N2
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
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 CO 2
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
Nitrogen Fixation R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N2ON2O N2N2
Nitrogen Fixation Energy intensive process : N 2 + 8H+ + 8e ATP = 2NH 3 + H ADP + 16 Pi Performed only by selected bacteria and actinomycetes Performed in nitrogen fixing crops (ex: soybeans)
Microorganisms fixing Azobacter Beijerinckia Azospirillum Clostridium Cyanobacteria Require the enzyme nitrogenase Inhibited by oxygen Inhibited by ammonia (end product)
Rates of Nitrogen Fixation N 2 fixing systemNitrogen Fixation (kg N/hect/year) Rhizobium-legume Cyanobacteria- moss30-40 Rhizosphere associations 2-25 Free- living1-2
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 northern bogs Cyanobacteria found in waterlogged soils
Nitrification R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N2ON2O N2N2
Nitrification Two step reactions that occur together : 1 rst step catalyzed by Nitrosomonas 2 NH O 2 2 NO H 2 O+ 4 H + 2 nd step catalyzed by Nitrobacter 2 NO O 2 2 NO 3 -
Optimal pH is between If pH < 6.0 rate is slowed If pH < 4.5 reaction is inhibited In which type of wetlands do you thing Nitrification occurs?
Denitrification R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N2ON2O N2N2
Denitrification Removes a limiting nutrient from the environment 4NO C 6 H 12 O 6 2N H 2 0 Inhibited by O 2 Not inhibited by ammonia Microbial reaction Nitrate is the terminal electron acceptor
Looking at the Nitrogen cycle through the eye of NH 4
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
Surfac e water Oxidized layer Reduce d soil layer [NH 4 ] HIGH Low [NH 4 ] Slow Diffusion nitrificatio n [NO 3 ] high
Surfac e water Oxidized layer Reduce d soil layer [NO 3 ] high Leaching [NO 3 ] Low N2N2 Denitrificatio n