The Soil Ecosystem

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The Soil Ecosystem

• Soil Organisms
• prepared by
• Dr. Roger Clay

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• Reading Charman Murphy has no appropriate
  reading.

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Organic Matter

• Litter
• Humus
• Soil organisms

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Role of Soil Organisms

• humification of litter
• slow, but continuous, breakdown of humus
• release of plant nutrients
• mixing of mineral organic matter
• increasing pore space
• ped formation
• improvement of water infiltration percolation
• nitrogen fixation
• mutualistic associations with higher plants

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Producers

• Minor part of biomass - must be close to surface.
• However, cyanobacteria (blue-green algae) can be
  important for N fixation.
• Green algae.
• Chemoautotrophs - oxidation of inorganic
  compounds, eg. nitrifying bacteria.
• Roots of plants - pore space, upward movement of
  minerals and a food source.

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Consumers

• Sometimes described as an organism which feeds on
  other living organisms - a rather artificial
  distinction.
• Biophages feed on - roots, fresh litter,
  microorganisms, soil fauna, or may be parasitic.
• Saprophages feed on - dead plant animal
  material.

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Major Consumers in Soil
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Major Consumers in Soil(cont.)
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Consumers - how abundant?

• Northern Hemisphere data indicate
• - a wide range of values
• - great importance of nematodes
• - importance of mites collembola, also in
  Aust.
• - annelids fairly imp., but likely to be less so
  in Aust. (giant earthworms)
• - lack of termites, very important in Aust.

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Consumers - biomass (g/m2)
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Consumers

• Generally lack the enzymes to be true
  decomposers.
• Termites earthworms are important exceptions.
• Ants are very important in Aust. (biomass,
  abundance influence)

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Decomposers

• Procaryotes - bacteria actinomycetes
• Eucaryotes - fungi
• Possess the necessary enzymes, eg. cellulase, to
  breakdown the most resistant components of
  litter.
• Require moist soil for activity (see figure)
• Have a much greater biomass than consumers (see
  table).

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The effect of moisture on decomposer activity
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Biomass (g/m2) of decomposres
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Mycorrhizal fungi

• Important mutualists with roots of many plant
  species.
• Ecto- endomycorrhizas.
• Some fungal species are generalists, but others
  are highly specialised.

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Mycorrhizal fungi (cont.) - benefits

• To the fungus
• - photosynthetic products.
• To the plant
• - increased root surface area (water
  nutrients)
• - more efficient uptake of phosphorus
• - protection from pathogens.

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Mycorrhizal infection growth of pine seedlings
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Termites in Aust.

• Important in most areas (partic. tropical
  sub-tropical).
• High biomass abundance, eg.
• tropical savanna 1000-2000/m2
• SA dry sclerophyll forest 600/m2

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Termites in Aust. (cont.)

• Feed on cellulose - gut protozoa provide
  cellulase.
• Rapid turnover of plant material, eg. SA dry
  sclerophyll - 1 sp. annually consumed 27 of all
  wood litter.
• Major nutrient recyclers, eg. tropical savanna in
  Qld. - recycling equivalent to 300-400kg of
  fertiliser per annum.
• Form clay-humus complexes (soil physical
  properties)..

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The Soil Ecosystem - Soil OrganismsMajor Ideas

• Soil organisms play important roles in soils.
• Producers are relatively unimportant.
• Soil organisms are diverse communities change
  with soil type, vegetation, etc.
• Decomposers are very important and are the bulk
  of the biomass.
• Decomposers have the enzymes necessary for
  breakdown of complex polymers.

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The Soil Ecosystem - Soil OrganismsMajor Ideas
(cont.)

• Mutualistic associations (partic. Mycorrhizas
• higher plants) are important.
• Termites (decomposers) are widespread important
  in Aust.