Biological Weathering

1. Biology

2. The Little Guys

3. CO2
O2
Detritus (Plant Debris)
Fungi
Earthworms
Bacteria
Soil Humus
energy

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

7. CH2O  CO2
NH4
+
 NO3
-
Fe2+
 Fe3+
H2S  SO4
2-
NO3
-
 NH4
+
Fe3+
 Fe2+
SO4
2-
 H2S
O2  H2O
Energy
Yield
Electron Donor
(food)
Electron Acceptor
Edonor - Eacceptor
EnergyEnergy

8. CH2O
CO2
O2
H2O
NO3
-CH2O
CO2 N2
Fe(OH)3
CH2O
CO2 Fe2+
CH2O
CO2
SO4
2-
H2S
Energy Yields
Donor Acceptor
700
400
100
Eh (mV)* Condition
oxic
suboxic
anoxic
*pH 7

9. Aerobic Organisms
Food Source
• Organic carbon*
• Ammonium Ion (NH4
+
)
• Ferrous Iron (Fe2+
)
• Hydrogen Sulfide (H2S)
Electron Acceptor
• Molecular Oxygen (O2)

10. CH2O  CO2
NH4
+
 NO3
-
Fe2+
 Fe3+
H2S  SO4
2-
O2  H2O
Energy
Yield
Electron Donor
(food)
Electron Acceptor
Energy
-400
-36
KJ/mol

11. 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 (SO4
2-
)

12. CH2O  CO2
NO3
-
 NH4
+
Fe3+
 Fe2+
SO4
2-
 H2S
O2  H2O
Energy
Yield
Electron Donor
(food)
Electron Acceptor
Energy
-400
-36
KJ/mol

13. Microorganism-PlantMicroorganism-Plant
RelationshipsRelationships

14. legumes
Bacterial-Plant Symbiosis

15. - 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

18. N-Fixation: Frankia
Frankia Nodules on Alder
- actinomycetes
- associates with desert
shrubs (e.g., Ceanothus)
and various tree species
(e.g., alder)

19. 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

20. EctomycorrhyzaeEctomycorrhyzae
- association at exterior of root
- develop on evergreen trees and shrubs

21. MycorrhizaeMycorrhizae
- Associations occur in root interior between cells
- Develop on deciduous trees, annual and herbaceous plants
Endomycorrhizae

22. Organic Matter Degradation
(Carbon Cycling)

23. CO2 Detritus (Plant Debris)
Fungi Earthworms
Bacteria
Soil Humus
Organic Matter
Biomass
Humin
(insoluble)
Humic Acid
(insoluble in acid)
Fulvic Acid
(soluble)
degradation
(nonliving, nontissue decay products)
(identifiable dead tissue)
(living organisms)

24. Pools of Soil Organic Matter

25. Soil Humus
Organic Matter Degradation: Nutrient Cycling
Biomass
Detritus (Plant Debris)
Nutrient
Release
Nutrient
Incorporation

26. -reactive functional groups:
-carboxyl, hydroxyl, phenolic
Soil Organic Matter: Humus
- High cation (anion) exchange capacity
- High water holding capacity
- Promotes soil aggregation

27. To continue…

28. Fertilizer Effects on Soil Organic Matter

29. Effect of manure on organic matter