Soil Biology and Ecology
14 | Unit 2.3
Students’ Lecture Outline
vi. Minor comminution
vii. 500 to 200,000 per square meter, far less biomass than microfauna
d) Macrofauna
i. Earthworms
• 3 ecological types (anecic, endogeic, epigeic)
• Vermisphere concept
• Obtain a portion of their nutrition from microbes living on organic residues they
ingest
• 7,000+ species
• Stimulate microbial activity through effects on SOM, microbial inoculation onto
substrates, soil structure, etc.
• Mix and aggregate soil
• Increase water infiltration
• Provide channels for root penetration deep into soil
• Bury and shred organic matter
• Abundance decreases after disturbance (tillage, chemicals)
ii. Millipedes, isopods, mollusks, insects
iii. Shred and incorporate plant remains (may become pests by feeding on living plants
if insufficient organic residues present)
iv. Alter soil structure
e) Megafauna
i. Large invertebrates, vertebrates
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 greater than 1 (i.e., more biota in R than in S)
e) Rhizosphere succession: The sequence of changes in the composition and densities of
soil microbes and fauna in the area surrounding a growing root (see below)
- Roots
a) Root environment
i. Determined by above-ground processes (products of photosynthesis are
translocated to roots)
ii. Exudates, sloughed hairs, and cells feed soil organisms in R and r
iii. Bicarbonate formation as a result of influences on pH
iv. Type and amount of exudates vary with species, age, soil
v. Oxygen decreases, CO 2 increases in root zone over time due to plant and R organism
respiration