3. Nitrification?

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3. Nitrification?

• 3.1 Biological conversion of nitrogen in
  organic and inorganic compounds from a reduced
  to a more oxidized state.

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3.2 Autotrophic Nitrification
3.2.1

• NH4 1.5 O2(aq) NO2- H2O 2H
• Nitrosomonas (ellipsoidal)

a.
NO2- 0.5 O2(aq) NO3- Nitrobacter
(short rods)

• Dominant organisms
• But also
• Nitrosococcus, Nitrospira, Nitrosolobus

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3.2 Autotrophic Nitrification
3.2.1

• NH4 NH2OH (H2N2O2) NO2- NO3-

b.
N2O

• aerobic
• obligate aerobes,
• non-spore forming,
• use inorganic C (carbon dioxide, carbonates,
  bicarbonate, methane)
• derive energy from oxidation of N.

3.2.2
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3.2 Autotrophic Nitrification

• Number in the soil
• 0 107 / g dry soil

3.2.3

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3.2 Autotrophic Nitrification

• Environmental influences?
• substrate N --- NH4 availability
• pH
• optimum 6.6 8
• falls off below 6 but there is considerable
  nitrification in acid soils at 4.5 (eg, red
  alder)
• oxygen
• required,
• best at 1/2 - 2/3 field capacity
• occurs in submerged soils because of oxygen
  diffusion

3.2.4
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3.2 Autotrophic Nitrification

• Environmental influences (contd)
• temperature
• range 5 40 C
• optimum 30-35 C
• inhibitory compounds
• phenolics from roots -
• suggestion that nitrification in later
  successional stages is inhibited by inhibitory
  compounds (allelopathic)

3.2.4
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3.2 Autotrophic Nitrification

• inhibition by chemicals -
• N-SERVE (nitrapyrin) commercially used
• conservation of N fertilizer (agric)
• effectiveness of inhibition affected by
  texture, increasing pH OM, and temp (sometimes)

3.2.5
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3.2 Autotrophic Nitrification
large quantities of nitrate produced by
autotrophs
3.2.6
3.3 Heterotrophic Nitrification (C source is
organic)

• bacteria (Arthrobacter)
• actinomycetes
• fungi (Aspergillus)

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3.3 Heterotrophic Nitrification

• Derive no energy
• Aspergillus flavus produces nitrate and
  3-nitropropionic acid many microbial
  metabolites contain partially or highly oxidized
  N (eg, nitrosamine)
• Cannot nitrify to the extent as Nitrosomonas
  and Nitrobacter

3.3.1
3.3.2
3.3.3
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3.4 Nitrification in Forest Soils

• nitrate losses high in early stages of stand
  devlp, low in intermediate stages, higher in
  later stages
• loss of N to lower horizons but also N in grd
  H2O /or streams and potential for leaching base
  cations (eg, Ca Mg) from soils

3.4.6

• the concept of net and gross nitrification

3.4.7
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3.5 Techniques???

• incubation bags or cores
• resin bags
• tension (or zero tension) lysimeters
• 15N
• watershed approaches (budget)

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Watershed budgets
Integrates across all stands
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Soil acidification N saturation from weathering
of NH4 -bearing rock
Klamath mountains of northern California
Mica schist bedrock
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