1. LECTURE 14 Soil Organisms

2. 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).

3. 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.

4. 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.

5. 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

6. Conditions affecting growth of soil microorganisms Organic matter requirements Oxygen requirements Moisture & temperature Exchangeable calcium and pH

7. Benefits of soil organisms… Organic material decomposition. Breakdown of toxic compounds Inorganic transformations Nitrogen fixation Plant protection

8. 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

9. 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.