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Soil Biology (Nematodes (Functions (Bacterial feeders, Fungal feeders,…

- - - - N,P cycling
      - Rhyzobia/Legume symbiosis
        
        Nitrogenase
        
        Fixes atmospheric nitrogen
        
        Leghaemoglobin
        
        Removes oxygen at fixation sites
        
        Plant gets nutrient availability
        
        Rhizobia receives energy
      - Mycorrhizae
        
        Plant root/fungus association
        
        Majority of vascular plants
        
        Endomycorrhizae, Ectomycorrhizae
        
        Fungus receives organic matter
        
        Plant receives improved nutrient and water uptake
        
        Fungal hyphae increase root surface area
  - - - Reproductive response to nutrient input
    - - Use nutrients for cell maintenance
  - - - More organic matter near surface
    - - Need to retain cell turgor
      - Can overcome short term changes in water stress
      - Affects nutrient supply, mobility and leaching of organics
    - - Some microbes need oxygen
      - Better aeration closer to the surface
    - - Well-aerated soils - oxygen is electron acceptor
      - Poorly-aerated soils - Nitrate/ Iron (III)/Sulfate ions are electron acceptor
    - - Affects nutrient availability
      - Organisms have different pH tolerances
    - - Wide range of temperature tolerances
      - Thermophilic, mesophilic, psychrophilic
      - Above optimum temp, denaturing of cellular proteins and membranes may occur
      - Increasing temp by 10C doubles growth rate, up to optimum (30 - 35C)
    - - Affects growth of autotrophic organisms (near soil surface)
  - - - Prokaryotes
      - 10^6 - 10^9/g soil
      - Less than 50% microbial biomas
      - Heterotrophic
      - Decompose readily oxidisable (simple) organic matter
      - 0.5-1.5 um diameter (cocci)
    - - Up to 70% microbial biomass, 10^4-10^6/g soil
      - Hyphae/mycelium filaments
      - Decompose complex organic matter e.g lignin
      - Fungal hyphae 3-10um diameter
    - - Aerobic/Heterotrophic
      - Produce geosmins
      - Degrade a wide range of molecular weight organic matter including recalcitrant materials e.g lignin and cellulose
      - Similar features to both bacteria and fungi
        
        Cell wall and composition similar to bacteria
        
        Morphology similar to fungi
      - Actinomycete 1 um diameter
    - - Contains chlorophyll
      - 10 - 10^6/g soil
      - Autotrophic - not decomposers, dependent on photosynthesis
      - Some fix nitrogen
      - Produce polysaccarides - structurally important
    - - 10^3 - 10^9/g soil
      - Unicellular animals 10-50 um, up to 0.5mm
      - Predators and grazers
      - Aquatic organisms
        
        Travel in water films
      - Organisms grazed on depend on size (whether protozoa fit into pore in which bacteria exist) but mainly bacteria and other protozoa