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GES 175, GES 175, Science of Soils Science of Soils Lecture 6, Soil Biology

GES 175, Science of Soils Lecture 6, Soil Biology

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Page 1: GES 175, Science of Soils Lecture 6, Soil Biology

GES 175, GES 175, Science of SoilsScience of Soils

Lecture 6, Soil Biology

Page 2: GES 175, Science of Soils Lecture 6, Soil Biology

The Little Guys

Page 3: GES 175, Science of Soils Lecture 6, Soil Biology

CO2

O2

Detritus (Plant Debris)

FungiEarthworms

Bacteria

Soil Humus

energy

Page 4: GES 175, Science of Soils Lecture 6, Soil Biology

Soil Bacteria

Ruehr’s Rule: “The bugs get it first”.

Page 5: GES 175, Science of Soils Lecture 6, Soil Biology
Page 6: GES 175, Science of Soils Lecture 6, Soil Biology
Page 7: GES 175, Science of Soils Lecture 6, Soil Biology

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

Page 8: GES 175, Science of Soils Lecture 6, Soil Biology

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

Page 9: GES 175, Science of Soils Lecture 6, Soil Biology

Aerobic Organisms

Food Source

• Organic carbon*

• Ammonium Ion (NH4+)

• Ferrous Iron (Fe2+)

• Hydrogen Sulfide (H2S)

Electron Acceptor

• Molecular Oxygen (O2)

Page 10: GES 175, Science of Soils Lecture 6, Soil Biology

CH2O CO2

NH4+ NO3

-

Fe2+ Fe3+

H2S SO42-

O2 H2O

EnergyYield

Electron Donor(food)

Electron Acceptor

Energy

-400

-36

KJ/mol

Page 11: GES 175, Science of Soils Lecture 6, Soil Biology

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-)

Page 12: GES 175, Science of Soils Lecture 6, Soil Biology

CH2O CO2

NO3- NH4

+

Fe3+ Fe2+

SO42- H2S

O2 H2O

EnergyYield

Electron Donor(food)

Electron Acceptor

Energy

-400

-36

KJ/mol

Page 13: GES 175, Science of Soils Lecture 6, Soil Biology

Microorganism-Plant Microorganism-Plant RelationshipsRelationships

Page 14: GES 175, Science of Soils Lecture 6, Soil Biology

legumes

Bacterial-Plant Symbiosis

Page 15: GES 175, Science of Soils Lecture 6, Soil Biology

- 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

Page 16: GES 175, Science of Soils Lecture 6, Soil Biology
Page 17: GES 175, Science of Soils Lecture 6, Soil Biology
Page 18: GES 175, Science of Soils Lecture 6, Soil Biology

N-Fixation: Frankia

Frankia Nodules on Alder

- actinomycetes

- associates with desert shrubs (e.g., Ceanothus) and various tree species (e.g., alder)

Page 19: GES 175, Science of Soils Lecture 6, Soil Biology

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

Page 20: GES 175, Science of Soils Lecture 6, Soil Biology

EctomycorrhyzaeEctomycorrhyzae

- association at exterior of root

- develop on evergreen trees and shrubs

Page 21: GES 175, Science of Soils Lecture 6, Soil Biology

MycorrhizaeMycorrhizae

- Associations occur in root interior between cells

- Develop on deciduous trees, annual and herbaceous plants

Endomycorrhizae

Page 22: GES 175, Science of Soils Lecture 6, Soil Biology

Organic Matter Degradation

(Carbon Cycling)

Page 23: GES 175, Science of Soils Lecture 6, Soil Biology

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)

Page 24: GES 175, Science of Soils Lecture 6, Soil Biology

Pools of Soil Organic Matter

Page 25: GES 175, Science of Soils Lecture 6, Soil Biology

Soil Humus

Organic Matter Degradation: Nutrient Cycling

Biomass

Detritus (Plant Debris)

Nutrient Release

NutrientIncorporation

Page 26: GES 175, Science of Soils Lecture 6, Soil Biology

-reactive functional groups: -carboxyl, hydroxyl, phenolic

Soil Organic Matter: Humus

- High cation (anion) exchange capacity

- High water holding capacity

- Promotes soil aggregation

Page 27: GES 175, Science of Soils Lecture 6, Soil Biology

To continue…

Page 28: GES 175, Science of Soils Lecture 6, Soil Biology

Fertilizer Effects on Soil Organic Matter

Page 29: GES 175, Science of Soils Lecture 6, Soil Biology

Effect of manure on organic matter