Transcript soil biology - Stanford University

GES 175, Science of Soils
Lecture 6, Soil
Biology
The Little Guys
O2
energy
CO2
Detritus (Plant Debris)
Earthworms
Fungi
Bacteria
Soil Humus
Soil Bacteria
Ruehr’s Rule: “The bugs get it first”.
Electron Donor
(food)
Electron Acceptor
CH2O  CO2
Edonor - Eacceptor
SO42-  H2S
NH4+  NO3Fe3+  Fe2+
Fe2+  Fe3+
NO3-  NH4+
H2S  SO42O2  H2O
Energy
Energy
Yield
Energy
*pH 7
Energy Yields
Donor
CH2O
Acceptor
CO2
H2O
CH2O
-
CO2
CH2O
CO2
CH2O
CO2
Condition
700
O2
NO3
Eh (mV)*
oxic
N2
400
Fe(OH)3
suboxic
Fe2+
SO42H2S
100
anoxic
Aerobic Organisms
Food Source
• Organic carbon*
• Ammonium Ion (NH4+)
• Ferrous Iron (Fe2+)
• Hydrogen Sulfide (H2S)
Electron Acceptor
• Molecular Oxygen (O2)
Electron Donor
(food)
Electron Acceptor
Energy
Yield
CH2O  CO2
KJ/mol
NH4+  NO3-
-400
Fe2+  Fe3+
H2S  SO42O2  H2O
Energy
-36
Anaerobic Organisms
Food Source
Electron Acceptor
• Organic carbon*
• Nitrate (NO3-)
• Ammonium Ion (NH4+)
• Manganese (Mn4+)
• Ferrous Iron (Fe2+)
•Ferric Iron (Fe3+)
• Hydrogen Sulfide (H2S)
• Sulfate (SO42-)
Electron Donor
(food)
Electron Acceptor
Energy
Yield
KJ/mol
CH2O  CO2
-36
SO42-  H2S
Fe3+  Fe2+
NO3-  NH4+
O2  H2O
Energy
-400
Microorganism-Plant
Relationships
Bacterial-Plant Symbiosis
legumes
Nitrogen Fixation
* Symbiotic relation between
bacteria and plants:
-e.g., legumes + Rhizobium
- bacteria require plant for growth; plant
gains ‘free’ source of available N
* Grasses-Azospirillum/Azobactor
N-Fixation: Frankia
- actinomycetes
- associates with desert
shrubs (e.g., Ceanothus)
and various tree species
(e.g., alder)
Frankia Nodules on Alder
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
Ectomycorrhyzae
- association at exterior of root
- develop on evergreen trees and shrubs
Mycorrhizae
Endomycorrhizae
- Associations occur in root interior between cells
- Develop on deciduous trees, annual and herbaceous plants
Organic Matter Degradation
(Carbon Cycling)
Organic Matter
(living organisms)
Biomass
Detritus (Plant Debris)
Fungi
(identifiable dead tissue)
Earthworms
Bacteria
Soil Humus
Humin
(insoluble)
(nonliving, nontissue decay products)
Humic Acid
(insoluble in acid)
Fulvic Acid
(soluble)
degradation
CO2
Pools of Soil Organic Matter
Organic Matter Degradation: Nutrient Cycling
Biomass
Nutrient
Incorporation
Detritus (Plant Debris)
Nutrient
Release
Soil Humus
Soil Organic Matter: Humus
-reactive functional groups:
-carboxyl, hydroxyl, phenolic
- High cation (anion) exchange capacity
- High water holding capacity
- Promotes soil aggregation
To continue…
Fertilizer Effects on Soil Organic Matter
Effect of manure on organic matter