ges 175, science of soils lecture 6, soil biology
TRANSCRIPT
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GES 175, GES 175, Science of SoilsScience of Soils
Lecture 6, Soil Biology
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The Little Guys
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CO2
O2
Detritus (Plant Debris)
FungiEarthworms
Bacteria
Soil Humus
energy
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Soil Bacteria
Ruehr’s Rule: “The bugs get it first”.
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CH2O CO2
NH4+ NO3
-
Fe2+ Fe3+
H2S SO42-
NO3- NH4
+
Fe3+ Fe2+
SO42- H2S
O2 H2O
EnergyYield
Electron Donor(food)
Electron Acceptor
Edonor - Eacceptor
EnergyEnergy
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CH2O
CO2
O2
H2O
NO3-CH2O
CO2 N2
Fe(OH)3CH2O
CO2 Fe2+
CH2O
CO2
SO42-
H2S
Energy YieldsDonor Acceptor
700
400
100
Eh (mV)* Condition
oxic
suboxic
anoxic
*pH 7
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Aerobic Organisms
Food Source
• Organic carbon*
• Ammonium Ion (NH4+)
• Ferrous Iron (Fe2+)
• Hydrogen Sulfide (H2S)
Electron Acceptor
• Molecular Oxygen (O2)
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CH2O CO2
NH4+ NO3
-
Fe2+ Fe3+
H2S SO42-
O2 H2O
EnergyYield
Electron Donor(food)
Electron Acceptor
Energy
-400
-36
KJ/mol
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Anaerobic Organisms
Food Source
• Organic carbon*
• Ammonium Ion (NH4+)
• Ferrous Iron (Fe2+)
• Hydrogen Sulfide (H2S)
Electron Acceptor
• Nitrate (NO3-)
• Manganese (Mn4+)
•Ferric Iron (Fe3+)
• Sulfate (SO42-)
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CH2O CO2
NO3- NH4
+
Fe3+ Fe2+
SO42- H2S
O2 H2O
EnergyYield
Electron Donor(food)
Electron Acceptor
Energy
-400
-36
KJ/mol
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Microorganism-Plant Microorganism-Plant RelationshipsRelationships
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legumes
Bacterial-Plant Symbiosis
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- bacteria require plant for growth; plant gains ‘free’ source of available N
Nitrogen FixationNitrogen Fixation
* Symbiotic relation between * Symbiotic relation between bacteria and plants:bacteria and plants:
-e.g., legumes + -e.g., legumes + RhizobiumRhizobium
* Grasses-Azospirillum/Azobactor
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N-Fixation: Frankia
Frankia Nodules on Alder
- actinomycetes
- associates with desert shrubs (e.g., Ceanothus) and various tree species (e.g., alder)
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Fungi-Plant Interaction
Mycorrhizae(root fungus)
- extension of root system
- fungus enhances nutrient and water intake
- plants provide carbon source
Nearly 90% of native plants have mycorrhizae association
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EctomycorrhyzaeEctomycorrhyzae
- association at exterior of root
- develop on evergreen trees and shrubs
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MycorrhizaeMycorrhizae
- Associations occur in root interior between cells
- Develop on deciduous trees, annual and herbaceous plants
Endomycorrhizae
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Organic Matter Degradation
(Carbon Cycling)
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CO2 Detritus (Plant Debris)
Fungi EarthwormsBacteria
Soil Humus
Organic Matter
Biomass
Humin(insoluble)
Humic Acid(insoluble in acid)
Fulvic Acid(soluble)
degr
adat
ion
(nonliving, nontissue decay products)
(identifiable dead tissue)
(living organisms)
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Pools of Soil Organic Matter
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Soil Humus
Organic Matter Degradation: Nutrient Cycling
Biomass
Detritus (Plant Debris)
Nutrient Release
NutrientIncorporation
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-reactive functional groups: -carboxyl, hydroxyl, phenolic
Soil Organic Matter: Humus
- High cation (anion) exchange capacity
- High water holding capacity
- Promotes soil aggregation
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To continue…
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Fertilizer Effects on Soil Organic Matter
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Effect of manure on organic matter