1ESC 590.Soil Biota.1

Soil BiotaSoil Biota

Reading AssignmentReading Assignment

Soil Microbiology: Soil Microbiology: An exploratoryAn exploratoryApproachApproach

Chapter 4, 5, 6 Chapter 4, 5, 6

The MacrofaunaThe Macrofauna

Examples Ants, Earthworm etc. Classified by » 1. Size» 2. Movement» 3. Time spent in soil or habitat» 4. What they eat


Based on what they eat

- 1. Biophagous» Carnivores

» Herbivores

» Microvores

» Omnivores


2. Saprophagous

» Detritivores

» Cadaveriocoles

» Copraphagous


Earthworms:» Often constitutes the major portion of the

invertebrate biomass in the soil.» Active in processing litter and distributing

organic matter throughout the soil.» Activities result in the improvement of soil

aeration , drainage, and structure.


Insects May be free-living, or may alternatively

live they may feed on plant roots


Significance » Agricultural importance of the macrofauna

rests upon its contribution to soil fertility, soil structure, and plant disease.

» Important in leaf and litter decomposition» Soil structure

The MesofaunaThe Mesofauna

Nematodes:» The most numerous of all metazoa. » Their numbers may reach several millions per

square meter.» Both parasitic and free-living groups are

encountered.» Free-living groups use organic debris,

microorganisms and other substances as food.

MicrofaunaMicrofauna

Protozoa» Predators of the other forms of microbes.» Enumerated with plate method» Important to microscopically examine» Environmentally source of food is only

concern.


» No effect of soil pH, except effect of food source

» Reproduce usually by asexual means -binary fission

» Vast majority are saprophytes i.e. use soluble organic and inorganic substances or phagotrophic i.e. characterized by a direct feeding of microbial cells or particulate matter.


» A few are autothrophic

» When edible prey cells are no longer avialable or the environment in some way is unfavourable, the active protozoan enters a cyst stage.

» Mostly aerobic


» Exhibit no marked sensitivity to pH. Opt pH 6-8.

» Prefers found cool damp environments

» Trpophozoite Cyst feeding (resting)

» Feed a lot of rhizobia


Classification:Classified on basis of locomotion (4

categories)

»1. Mastigophora

»2. Sarcodina

»3. Ciliphora

»4. Sporozoa


a. Flagella –Mastigophora» most abundant in soil» 5-20 um in length» dominate the microfauna of terrestial

habitats» tolerant of low moisture


b. Cilia -Ciliata (ciliophora)» Movement by action of vibrating hairs

situated around the protozoan cell.» abundant in areas with high moisture status


c. Pseudopoda-Sarcodina

» size range from 10 mm to 80 mm

» move by means of temporary protoplasmic extrusions from the cell body e.g Amoeba


Significance in Soil.» 1. Serve to regulate soil bacterial population» 2. May also function by allowing different

competing bacteria to coexist in soil.» 3. They may participate in the decomposition

of plant materials.» 4. Some are pathogenic e.g Entamoeba

histolytica which cases amoebic dysentry

VirusesViruses

• These incluse nematodes, millipedes centipedes, mites, spiders, insects earthworms, flatworms etc.

Viruses • The are submicroscopic agents • Consist of DNA or RNA molecules within protein coats. • Viral particles are metabolically inert and do not carry out respiratory or bio-

synthetic functions. • They induce a living host cell to produce the necessary viral components • After assembly, the replicated viruses escape from the cell with the capability of

attacking new cells. • Viruses infect all categories of animal and plants, from humans to microbes. • Those parasitizing bacterial cells commonly are called bacteriophages, or simply

phages Significance in Soil • Little is known about the field ecology of viruses that infect soil organisms except

that they persist in soil as domant units that retain parasitic activities. • The ability of viral particles pathogenic to plants or animals to survive in soil and

move into the water table is of major concern to people.

Documents

1ESC 590.Soil Biota.1