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Lecture 6, Soil Biology

GES 175, Science of Soils. Lecture 6, Soil Biology. The Little Guys. O 2. CO 2. energy. Detritus (Plant Debris). Earthworms. Fungi. Bacteria. Soil Humus. Soil Bacteria. Ruehr’s Rule: “The bugs get it first”. Energy Yield. Electron Donor (food). Electron Acceptor.

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Lecture 6, Soil Biology

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

  2. The Little Guys

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

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

  5. Energy Yield Electron Donor (food) Electron Acceptor CH2O  CO2 Edonor - Eacceptor SO42-  H2S NH4+ NO3- Fe3+ Fe2+ Fe2+ Fe3+ NO3- NH4+ H2S  SO42- O2  H2O Energy Energy

  6. Energy Yields *pH 7 Acceptor Eh (mV)* Condition Donor CH2O 700 O2 CO2 H2O oxic CH2O NO3- CO2 N2 400 CH2O Fe(OH)3 suboxic CO2 Fe2+ 100 CH2O SO42- anoxic CO2 H2S

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

  8. Energy Yield Electron Donor (food) Electron Acceptor CH2O  CO2 KJ/mol NH4+ NO3- -400 Fe2+ Fe3+ H2S  SO42- -36 O2  H2O Energy

  9. Anaerobic Organisms Food Source Electron Acceptor • Nitrate (NO3-) • Manganese (Mn4+) • Ferric Iron (Fe3+) • Sulfate (SO42-) • Organic carbon* • Ammonium Ion (NH4+) • Ferrous Iron (Fe2+) • Hydrogen Sulfide (H2S)

  10. Energy Yield Electron Donor (food) Electron Acceptor KJ/mol CH2O  CO2 -36 SO42-  H2S -400 Fe3+ Fe2+ NO3- NH4+ O2  H2O Energy

  11. Microorganism-Plant Relationships

  12. Bacterial-Plant Symbiosis legumes

  13. 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

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

  15. 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

  16. Ectomycorrhyzae - association at exterior of root - develop on evergreen trees and shrubs

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

  18. Organic Matter Degradation (Carbon Cycling)

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

  20. Pools of Soil Organic Matter

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

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

  23. To continue…

  24. Fertilizer Effects on Soil Organic Matter

  25. Effect of manure on organic matter

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