Carbon Cycle

  1. Description of Aerobic decomposition process
    • 1) Senescence
    • --Nutrients translocated out of leaves (as much as 70%
    • --sugars withdrawn
    • 2) Soluble components leach as leaves drop into water
    • 3) Fungi and bacteria colonize the tissue
    • 4) Complex macromolecules broken into pieces by exoenzymes secreted by microorganisms
  2. Description of Anaerobic decomposition process
    • 1) Complex macromolecules (like cellulose) cleaved by exoenzymes 
    • --This is often the limiting step
    • --slow b/c low energy yield of products hinders cell growth and exoenzyme synthesis
    • --sugars absorbed
    • 2)Fermentation
    • --When organic matter is the terminal electron acceptor in anaerobic respiration
    • 3) SO4 and CO2 are electron receptors
    • 4) Methane formation produced by methanogenic divisions of Archea
  3. Role of Exoenzymes
    an enzyme that is secreted by a cell and that works outside of that cell. It is usually used for breaking up large molecules that would not be able to enter the cell otherwise.
  4. Ways methane is formed: 
    • CH3COOH->CH4+CO2
    • 4H2+CO2->CH4+H20
  5. relative rates of decomposition of plant components
    • 1) Sugars-Fastest
    • 2) Protein
    • 3) Cellulose-wide range of bacteria and fungi
    • 4) Lignin- wood is high in lignin, needs O2 requiring enzymes to be broken down, several years to decay
    • 5) Humified residues flormed during decomposition - Slowest
  6. Factors Controlling Decomposition
    • 1) Substrate
    • --Higher lignin content=slower decomposition
    • --Soluble matter=fast decomposition
    • --Amount of polyphenols and organic N
    • 2) Temperature
    • --Respiration of soil is exponentially related to temp over range of -5C and 25C
    • --As temp approaches the respiration max at 25C the curve begins to level out.
    • 3) Moisture-
    • 4) Nutrients- inorganic N stimulates decomp.
    • 5) pH ~ 5 and below inhibits decomposition
Card Set
Carbon Cycle
Quiz 3