1. Soil Biology – A Primer* Who is who & What do they do?
* primer isn’t a complete review of Ch 11

2. Learning Objectives List the major groups of soil organisms …
Identify the roles of organisms
Draw a simplified soil food web ...
Describe the conditions affecting growth…
Discuss the beneficial functions …

3. Classification – A means to make sense of the diversity
Taxonomic groups (plants, animals, bacteria, fungi, protista)
Functional groups & size (microflora vs. macroflora/fauna) – Table 11.1
Carbon/energy source (detritivores vs. fungivores; autotrophic vs. heterotrophic) – Fig 11.1, Table 11.3
Environmental tolerance (thermophiles, anaerobes, etc.)
Predators, herbivores, detritivores
Autotrophs, heterotrophs
Anerobic, aerobic, facultative

4. Prokaryotes Eukaryotes Taxonomic groups: Bacteria Archaea Protists
Phylogenic Tree of Life
Prokaryotes
Bacteria
Archaea
Eukaryotes
Protists
Fungi
Plants
Animals
Fig c/o Diana Nemergut, INSTAAR
Source: Norman R. Pace. A Molecular View of Microbial Diversity and the Biosphere. SCIENCE VOL MAY p 734ff
(Pace 1997)

5. Biological Kingdoms Taxonomic groups:

6. Important Groups of Soil Organisms
Size, functional groups:
Important Groups of Soil Organisms
Macroflora
Microflora
Macrofauna
Vascular plants, mosses (autotrophs)
Vascular plants (root hairs), algae, actinomycetes, bacteria, and fungi
(auto- and heterotrophs)
Vertebrates, arthropods, earthworms, snails…
(herbivores, detritivores, predators)
Mesofauna
Microfauna
Arthropods, worms (detritivores, predators)
Nematodes, protazoa… (detritivores, fungivores, bacterivores, predators)

7. { { { A cup of soil contains... Bacteria 200 billion Fungi Microflora,
Size:
A cup of soil contains...
Bacteria
Fungi
Protozoa
Nematodes
Arthropods
Earthworms
200 billion {
Microflora,
or “microbes”
See text Table 11.1
100,000 meters {
20 million
Microfauna
100,000 {
50,000
Macro- and mesofauna
* Fungi, their own separate kingdom
<1
Immobile organisms all primarily found in the rhizosphere, the zone of soil closest to plant roots

8. Relative Sizes Animated gif – view in slideshow mode
Note ruler for scale
Web site: search “microbe zoo Dirtland”

9. Microflora
heterotrophs (bacteria, fungi) & autotrophs (algae, cyanobacteria)
the primary decomposers
release plant available nutrients
stabilize soil aggregates
Soil bacteria
Soil fungi

10. Aggregates held together by:
Microflora –
hyphae
clay
Aggregates held together by:
Fungal hyphae
Bacterial “glues”
Organic matter
sand
silt
bacteria

11. Fungi The major agent of decay in acid environs
Microflora –
Fungi
The major agent of decay in acid environs
Network of hyphae: improves soil structure
Decomposition of cellulose!!!
Can compete with higher plants for N
N.B. – Fungi are in their own separate kingdom from plants: they are non-photosynthetic, and their RNA is actually more like animals, than like plants.

12. Bacteria Exist in both forest and grassland soils
Microflora –
Bacteria
Exist in both forest and grassland soils
Aerobic, anaerobic, and facultative forms
Autotrophic and heterotrophic forms
Most do best under high Ca2+, high pH
Do best when soil temp 20-40C (68-100F) but seldom killed by temperature extremes

13. Fungi vs. bacteria Microflora – Fungi Bacteria
Single-celled, can form colonies
Tube-like body; hyphae
Aerobic, anaerobic, and facultative species
Aerobic only
Rapid regeneration time (hours); can respond quickly to nutrient additions
Generally slower growth rate

14. Microfauna Ciliate heterotrophs; some parasitic Flagellate
feed on bacteria and fungi
release plant nutrients – protozoa KEY for N
Flagellate
Amoebae
Nematode
Nematode
eeee!

15. Nematodes (non-segmented, round worms)
Microfauna –
Nematodes (non-segmented, round worms)
Widely distributed in forest soils
Saprophytic and parasitic groups
Some predatory species attack tree roots and cause damage

16. Protozoa Microfauna – Most abundant of all soil fauna One-celled
Feed on bacteria
Up to 30% of all mineralized N from protozoa

17. Mesofauna heterotrophs (detritivores, predators)
feed on fungi, protozoa, nematodes, mites
important in regulating populations of everything smaller
Fungus feeding mite
Nematode feeding mite
Collembola (springtails)

18. Macrofauna heterotrophs shred plant material
feed on bacteria and fungi associated with organic matter
Photo by Suzanne Paisley

19. Earthworms Macrofauna –
Probably the most important component of soil fauna (not in acid soils, not in very dry soils)
Pass as much as 30 tons/ha of soil through their bodies each year
Excreted casts higher in N, P, K, Ca, Mg, pH, & CEC
Promote good soil structure and aeration

20. Earthworm casts vs. soil
Macrofauna –
Earthworm casts vs. soil
Characteristic
Earthworm casts
Soils
silt & clay (%)
22.2
Bulk density (g/cm3)
1.28
Structural stability 65
CEC (cmolc/kg)
3.5
38.8
1.11
849
13.8
From text Table 11.6

21. Dung Beetles Macrofauna – Key disposer of elephant dung
and so a protected species!
(you can imagine the ‘or else’…)
Amboseli National Park, Kenya
by Andy Lyons
Amboseli National Park by Howard Norfolk
Tembe Elephant Reserve KwaZulu Natal, South Africa
Addo National Park, South Africa

22. By Mendenhall c/o American Greetings

23. Influence of soil biota on soil processes
Ecosystem Function –
Influence of soil biota on soil processes
Nutrient cycling
Soil structure
Microflora
Microfauna
Mesofauna
Macrofauna
Break up O.M., mineralize and immobilize nutrients
Bind aggregates, hyphae entangle particles
Regulate bacterial and fungal populations
Indirectly affect structure
Regulate above pops.; fragment plant tissue
Fecal pellets, pores
Fragment plant tissue
Mix O.M. and mineral soil; pores; feces

24. Recall: Rate of decomposition depends on –
Ecosystem Function –
Recall: Rate of decomposition depends on –
Physical and chemical nature of the litter material
Temperature and moisture of the soil environment
Aeration (vs. anaerobic)
The kinds and numbers of soil fauna
 More bugs, and more different kinds of bugs, means more decomposition

25. Ecosystem Function –
Soil Food Web
See also text Fig 11.1

26. Some generalizations . . . Forested soils more biologically diverse
Ecosystem geography –
Some generalizations . . .
Forested soils more biologically diverse
Forested soils dominated by fungi
Faunal biomass (and activity) greater per ha in grasslands
Cultivated soils least diverse, less biomass, fewer organisms
cf. text Table 11.4 (p. 453)