3' Mineralization

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(No Transcript)
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• 3. Mineralization
• (Ammonification or ammonium mineralization)
• Microbes take up DON and secrete N as NH4 if it
  is available in excess of available C

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Microbes only mineralize N when they are starved
for C!
Example Microbial CN 101 Microbial growth
efficiency 40 of C can be used for Growth (_at_
CN of 101) and 60 is respired as CO2
immobilize N from soil soln microbes break
even microbes mineralize N
Substrate CN 50 Substrate CN 25 Substrate
CN 15
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Attractively simple, but

• Microbe CN differs
• Among microbe taxa
• With temperature and moisture
• With resource availability

• Microbial growth efficiency differs
• Among microbe taxa
• With temperature and moisture
• With different substrates

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Mineralization terms
Gross NH4 mineralization Total amount of NH4
mineralized regardless of fate
Gross NH4 immobilization Total amount of NH4
taken up by microbes
Net NH4 mineralization Net accumulation of N
in soil solution that is presumably available for
plant uptake N in excess of microbial demand
Net NH4 immobilization Net reduction of N in
soil solution
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• Fate of NH4
• Immobilized microbes
• Taken up by a plant
• Adsorbed on soil exchange complex--available
• Stabilized on clays or SOM--unavailable
• Volatilized as ammonia (NH3)
• Oxidized by microbes to nitrite, nitrate (NO2-,
  NO3-)

What determines the fate of NH4?
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Schimel and Bennett 2004
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Schimel and Bennett 2004
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Schimel and Bennett 2004
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Transition to the phosphorus cycle

• Like N...
• Internal cycling of P dominates annual fluxes and
  P available for plant uptake

• Unlike N...
• Microbes and plants produce phosphatases
• extracellular enzymes that breakhydrolyze--ester
  linkages
• mineralize organic P outside of the cell
• Ester linkages that bind P to C can be cleaved
  without breaking down the C skeleton
• No oxidation-reduction reactions
• No gas phases

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Dust
Litter
Occluded P-inxn with mineral surfaces
Occluded P-2? minerals
SOP
PO43-
DOP
Rock
Erosion
Leaching
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Transition to the phosphorus cycle

• Like N...
• Internal cycling of P dominates annual fluxes and
  P available for plant uptake

• Unlike N...
• Microbes and plants produce phosphatases
• extracellular enzymes that break ester linkages
• mineralize organic P outside of the cell
• Ester linkages that bind P to C can be cleaved
  without breaking down the C skeleton
• No oxidation-reduction reactions
• No gas phases

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P input to soil Weathering Ca5(PO4)3 4H2CO3
? 5Ca2 3HPO42- 4HCO3- H2O
Apatite (mineral)
Bio-available P
Carbonic acid (CO2 from respiration)
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Fates of weathered phosphate

• Plant or microbial uptake, plant litter, soil
  organic matter (organic P)
• Adsorption on exchange site (non-occluded P,
  exchangable)
• Adsorption and incorporation into structure of Fe
  and Al oxides (occluded P)
• Precipitation with Fe, Al or Ca ions (occluded P)

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• P is unavailable to plants and microbes when...
• Phosphate is strongly adsorbed to the surface of
  soil minerals

• It becomes occluded--forms stable precipitates
  with calcium (high pH), iron, and aluminum (low
  pH)

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Fate is sensitive to soil pH
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Plants and microbes can influence P availability

• Produce phosphatases to hydrolyze O-P
• Secrete acids to
• Chelate metals (Al, Fe)
• Decrease pH in basic soils to solubilized P

Mineralize P when starved for P (contrast to N)
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Cluster roots
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• Forms of P in soil are dependent upon...
• Plants and microbes
• Soil parent material
• pH
• Ecosystem development and pedogenesis

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Soil profile - Oxisol
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Chadwick et al. 2000