Transcript LECTURE 14 Soil Organisms

LECTURE 14
Soil Organisms
Diversity…
• Size of organisms.
• Types of diversity
• Species diversity
• Functional diversity
• Ecosystem dynamics
• Functional redundancy (= ecosystem stability and
resilience)
• NB keystone species!
• Genetic resources (contribution to global
biodiversity).
Types of organisms…
• Primary producers
• Utilize water, energy and carbon to make
organic molecules and living tissues.
• Primary consumers
• Animals and microflora that use energy stored
in plant residues.
• Actions of microflora mostly biochemical, those
of microfauna both physical and chemical.
• Secondary consumers
• Bodies (i.e. cells) of primary consumers
become food sources for predators and
parasites.
• Include microflora (e.g. fungi) and carnivores.
• Tertiary consumers
• These organisms prey on secondary
consumers.
• Microflora NB in every level of the process.
Factors affecting organism
abundance…
• Food (amount & quality)
• Physical factors
– Moisture
– Temperature, etc.
• Biotic factors, e.g.
– Predation
– Competition
• Chemical characteristics of soil
– Acidity
– Dissolved nutrients
– Salinity
Conditions affecting growth
of soil microorganisms
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Organic matter requirements
Oxygen requirements
Moisture & temperature
Exchangeable calcium and pH
Benefits of soil organisms…
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Organic material decomposition.
Breakdown of toxic compounds
Inorganic transformations
Nitrogen fixation
Plant protection
Earthworms as an example of
important macro-organisms…
• 3000 species worldwide
• Influence soil fertility and productivity
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Burrows
Casts
Nutrients
Physical effects
• Factors affecting activity
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Air, temperature & water
Organic matter
pH
Predators
Texture
Fertilizer & Pesticides
Tillage
Soil Bacteria…
• Small, single-celled organisms
• Most diverse group of soil organisms
– 1g of soil typically contains 20 000 species!
– Can live in very diverse environments
• Can be autotrophs or heterotrophs
• Why are they important?
– Take part in almost all organic transactions that
characterize a healthy soil system.
– Nitrogen fixation.
– Cyanobacteria contain chlorophyll and can
photosynthesize.