Soil Biology and Ecology
12 | Unit 2.3
Students’ Lecture Outline
c) Energy loss = 80–90% at each step in the food chain
d) Food web structure and properties
i. Resilience = speed of recovery after disturbance
ii. Resilience decreases with increasing number of trophic levels due to increasing
complexity—takes longer to reestablish complex food web relationships
iii. Disturbance selects for shorter food chains: In farmed soils, disturbance can be
chemical (pesticides, fertilizers) or physical (cultivation, organic matter incorporation,
removal of surface organic layer)
iv. Relate to timing of agricultural inputs and other disturbances
v. Fungi:bacteria biomass ratio characteristics of soil ecosystems
• Productive agricultural soils ratio 1:1 or less (higher in no-till) = bacterial-
dominated food webs with rapid cycling of nutrients
• Deciduous forest, 5:1 to 10:1 (fungal dominated)
• Coniferous forest, 100:1 to 1000:1 (fungal dominated)
e) ways that soil animals interact with soil microorganisms and influence soil properties
i. Shredding of organic matter (comminution)—“can openers”
ii. Spreading to new habitats and new food resources (dissemination)
iii. grazing: Stimulate growth, control populations
iv. Predation: Similar effects as grazing
v. Soil structure changes (burrowing, mixing, defecating, crumb formation)
f ) Unique food web for each ecosystem, determined by:
i. Climate
ii. Soil/parent material
iii. Vegetation
iv. Land management practices
f. soil biota
- Characteristics
a) Diversity of organisms in soil can rival that of coral reef ecosystems
b) Characterized by small size and indistinct morphologies
c) Due to cryptic environment, visual cues are less important—bright colors and patterns
are lacking in soil organisms
d) Biomass comparisons
e) Abundance
- Habitats
a) Habitats within soil ecosystems are unevenly distributed
b) Habitats are concentrated at organic matter sites
i. Root zone (rhizosphere)
• Succession of organisms as root grows
• Some root exudates and root hairs may stimulate microorganisms by producing
labile SOM
ii. Litter
iii. Surface of soil aggregates
iv. Incorporated organic matter