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Transcript
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 • • • • Organic matter requirements Oxygen requirements Moisture & temperature Exchangeable calcium and pH Benefits of soil organisms… • • • • • 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 – – – – Burrows Casts Nutrients Physical effects • Factors affecting activity – – – – – – – 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.
