Mineralisation

Question 1

Decomposition steps:

Answer 1

1. Reduction of organic matter by detritivores
   
   2. Resistant tissue breakdown by fungi
   3. Decomposition of organic substances by fungi and bacteria
      Decomposition of dead organisms and faeces by micro-organisms

Question 2

Role of ecosystem engineers?

Answer 2

• Transport organic matter and micro-organisms through soil
  
  • Mix organic material and micro-organisms
  • Influence soil structure

Question 3

Humus:

Answer 3

• Contains most resistant substances
  
  • Contains OH and COOH groups
  • Negative charge - high CEC (because CEC depends on pH)
  • Below pH 7 (more acidic) - carboxyl exchange
    Above pH 7 (more basic) - carboxyl and hydroxyl exchange

Question 4

How does humus bond to metal ion?

Answer 4

Through chelation; humus is the ligand. Trivalent cations are more stable than divalent cations (stronger electrostatic bonds and chelate ring, and due to CFS)

Question 5

Importance of chelation?

Answer 5

Improves soil formation, removes heavy metals, and prevents unwanted reactions involving essential nutrients. Chelated minerals are also more rapidly absorbed

Question 6

What is a sesquioxide?

Answer 6

3 O and 2 metal atoms (3:2) e.g. Al2O3
- 50-90% organic matter bound to clay or sesquioxide
Extra bonds -> less decomposition

Question 7

Phenolic

Answer 7

one or more OH bonded to an aromatic ring
- Most resistant substances of OM
- Form chains
- Can only be broken down by phenol oxydase

Question 8

How do phenolics reduce decomposition?

Answer 8

Reduce decomposition of other organic molecules by interfering with enzymes.

Question 9

Immobilisation

Answer 9

when mineralised components are taken up by micro-organisms for production of biomass
Strong competition between micro-organisms and roots for nutrients (from mineralisation) - microbes win

Question 10

Can C from dissimilation be used for assimilation?

Answer 10

No because it is converted to co2 which disappears from the system