Soil Biology and Ecology
6 | Unit 2.3
Instructor’s Lecture Outline
d) See appendix 1, Major Organic Components of Typical Decomposer Food Sources,
for a comparison of the components of some typical decomposer food sources
e) Physical factors influence decomposition
f) Limiting factors
g) Plant secondary compounds may inhibit decomposition (polyphenols, tannins)
- Nitrogen cycle
a) Proteins —> amino acids —> ammonium —> nitrate
b) Ammonification aerobic or anaerobic
c) Nitrification aerobic
d) If C:N < 20–30:1 = net mineralization. If C:N > 20–30:1 = net immobilization
- Carbon and nitrogen mineralization exercise (handout)
E. Soil Food Webs
- Soil food web ecology
- Heterotrophic vs. autotrophic food webs
a) Autotrophic food webs —> begin with C fixation by plants
b) Heterotrophic food webs —> release nutrients required by all plants
c) Energy loss = 80–90% at each step in the food chain
d) Food web structure
e) Ways that soil animals interact with soil microorganisms
f) Unique food web for each ecosystem, determined by:
F. Soil Biota
- Characteristics
- Habitats
- Functional classification
a) Microorganisms
b) Microfauna
c) Mesofauna
d) Macrofauna
e) Megafauna
G. Rhizosphere Ecology
- Definitions
a) Rhizosphere (R) = the narrow zone of soil subject to the influence of living roots,
as manifested by the leakage or exudation of substances that promote or inhibit
microbial activity
b) Rhizoplane (r)= the actual root surface, which provides a highly favorable nutrient
base for many species of bacteria and fungi
c) Edaphosphere (S) = soil beyond root influence
d) Rhizosphere effect = soil microorganisms and fauna stimulated
i. —> R/S ratio generally increases
e) Rhizosphere succession = the sequence of changes in the area surrounding a growing
root