Chapter 7: Organisms

 

A biological universe exists in a gram of soil.

Biological Classification

 

A soil aggregate or ped is a naturally formed assemblage of sand, silt, clay, organic matter, root hairs, microorganisms and their secretions, and resulting pores.

A soil aggregate or ped is a naturally formed assemblage of:

  • sand
  • silt
  • clay
  • organic matter
  • root hairs
  • microorganisms and their secretions
  • pores

 

 

Soil Biota

Consists of:

  • bacteria
  • fungi
  • algae
  • soil animals
  • plants

Millions of species of soil organisms exist but only a fraction of them have been identified.

 

Soil biota can be grouped by size classes:

  • macrofauna (cm)
  • mesofauna (mm
  • microfauna (μm)

 

 

Soil Communities

 

 

 Extremophiles

 

Requirements and Adaptations of Microbes

 

Nutritional Requirements of Organisms in General

Kinds of Organisms in the Soil

Kind Food Energy source
Large Eucaryotes
  • Animals
  • Plants


Solid organic
CO2 + ions
 

Oxidation of organics
Light

Small Eucaryotes
  • Protozoas
  • Algae
  • Fungi


Solid & dissolved organics
CO2 + ions
Dissolved organics

 



Oxidation of organics
Light
Oxidation of organics
Bacteria
  • Phototrophic
  • Chemotrophic
  • Heterotrophic
 

CO2 + ions
CO2 + ions
Dissolved organics

 

 

Light
Oxidation of inorganics
Oxidation of organics

 

Reduction
Oxidation
Heterotrophs
Autotrophs

 

Heterotrophic organisms get energy from reactions involving organic substrates such as sugars.

 

The energy is released by:

  • respiration
  • fermentation

 

 

 

Plant root systems function heterotrophically but the plant as a whole is autotrophic.

Oxidation Processes That Supply Energy to Microbes

Reductant Oxidant Products Organism/conditions
Sugars and other organic compounds

Oxygen

CO2 Most organisms, aerobic
Sugars and other organic compounds   CO2, N2, N2O Denitrifiers*, low O2
Sugars and other organic compounds   CO2, S S reducers**, low O2
Sugars and other organic compounds Oxygen CO2, organic acids Anerobic fermenters/low O2
NH4+, NO2- Oxygen N2O-, NO3- Nitrifiers/aerobic
S Oxygen SO42- S oxidizers/aerobic
Fe2+ Oxygen Fe3+ Iron bacteria/aerobic
       

* Denitrifier: microbial process of nitrate reduction

** (S)ulfur reducers: get their energy by reducing elemental sulfur to hydrogen sulfide

 

 

 

Heterotrophs and autotrophs depend on each other.

The cycling of nutrient elements depend on these organisms.

 

 

 

Large Organisms

Plants & Their Roots

 

 

 

Roots:

  • Meristem
  • Stele
  • Xylem
  • Phloem
  • Root hairs
  • Epidural cells

 

The rhizosphere contains a dynamic and continuously changing biological community that may include:

and larger organisms such as:

 

Soil Biology Movies

 

 

Transparent Soil

transparent soil, nafion, university of abertay dundee, uk, roots, rhizosphere, James Hutton Institute

 

 

root, tip, microscope, rhizosphere, nafion, transparent soil