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GES 175, Science of Soils Lecture 6, Soil Biology
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The Little Guys
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CO 2 O2O2 Detritus (Plant Debris) Fungi Earthworms Bacteria Soil Humus energy
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Soil Bacteria Ruehr’s Rule: “The bugs get it first”.
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CH 2 O CO 2 NH 4 + NO 3 - Fe 2+ Fe 3+ H 2 S SO 4 2- NO 3 - NH 4 + Fe 3+ Fe 2+ SO 4 2- H 2 S O2 H2OO2 H2O Energy Yield Electron Donor (food) Electron Acceptor E donor - E acceptor Energy
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CH 2 O CO 2 O2O2 H2OH2O NO 3 - CH 2 O CO 2 N2N2 Fe(OH) 3 CH 2 O CO 2 Fe 2+ CH 2 O CO 2 SO 4 2- H2SH2S Energy Yields Donor Acceptor 700 400 100 Eh (mV)*Condition oxic suboxic anoxic *pH 7
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Aerobic Organisms Food Source Organic carbon* Ammonium Ion (NH 4 + ) Ferrous Iron (Fe 2+ ) Hydrogen Sulfide (H 2 S) Electron Acceptor Molecular Oxygen (O 2 )
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CH 2 O CO 2 NH 4 + NO 3 - Fe 2+ Fe 3+ H 2 S SO 4 2- O2 H2OO2 H2O Energy Yield Electron Donor (food) Electron Acceptor Energy -400 -36 KJ/mol
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Anaerobic Organisms Food Source Organic carbon* Ammonium Ion (NH 4 + ) Ferrous Iron (Fe 2+ ) Hydrogen Sulfide (H 2 S) Electron Acceptor Nitrate (NO 3 - ) Manganese (Mn 4+ ) Ferric Iron (Fe 3+ ) Sulfate (SO 4 2- )
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CH 2 O CO 2 NO 3 - NH 4 + Fe 3+ Fe 2+ SO 4 2- H 2 S O2 H2OO2 H2O Energy Yield Electron Donor (food) Electron Acceptor Energy -400 -36 KJ/mol
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Microorganism-Plant Relationships
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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 Fixation * Symbiotic relation between bacteria and plants: -e.g., legumes + Rhizobium * 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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Ectomycorrhyzae - association at exterior of root - develop on evergreen trees and shrubs
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Mycorrhizae - 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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CO 2 Detritus (Plant Debris) FungiEarthworms 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)
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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 Nutrient Incorporation
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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
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