- Soil is a complex 3D habitat that supports abundant and diverse forms of life. Soil organisms perform essential ecosystem functions. - The living component of soil includes bacteria, fungi, protists, nematodes, arthropods and other organisms that exist in huge numbers in a small amount of soil. - Soil organisms drive key ecosystem processes like decomposition, nutrient cycling, carbon storage, and soil structure/aggregation through production of glues and polysaccharides. Their activities create a habitat for other organisms and support life above ground.

1. Module 3: Soil Biology
The Living Component of Soil

2. Essential Questions and Big Ideas
Essential Questions
• What types of life exist in the soil?
• What ecosystem services do these organisms perform?
Big Ideas
• Soil is a complex and 3-dimensional habitat whose properties
change with space and time.
• Abundant and diverse forms of life exist in this habitat.
• Soil organisms perform essential ecosystem functions such as
decomposition of organic compounds, carbon and nutrient cycling,
and soil structuring.
Soil Science Society of America www.soils.org | www.soils4teachers.org
NGSS:
HS ESS2-7
HS LS1-5
HS LS1-7

3. Big Idea 1
Soil is a complex and 3-dimensional habitat
whose properties change with space and
time
Soil Science Society of America www.soils.org | www.soils4teachers.org

4. Soil at Different Scales
Soil Science Society of America www.soils.org | www.soils4teachers.org

5. Soil as a Habitat
Soil Science Society of America www.soils.org | www.soils4teachers.org
https://youtu.be/MlREaT9hFCw

6. Soil as a Habitat
Soil is a heterogeneous 3D environment
• Solid minerals and organic matter
• 3D pore network filled with liquids and/or gas
o Gases and water
o Nutrient and waste exchange
o Movement for larger organisms
• Massive surface area for life
• Physical separation
• Steep chemical gradients over small scales
What characteristics of organisms would allow them to be successful in this habitat?
An amoeba squeezing through
a soil pore
Erktan et al. 2020. https://doi.org/10.1016/j.soilbio.2020.107876

7. Big Idea 2
Abundant and diverse forms of life exist in
the soil habitat
Soil Science Society of America www.soils.org | www.soils4teachers.org

8. How Many Microbes?
Soil Science Society of America www.soils.org | www.soils4teachers.org
In one hectare (2.5 acres) of topsoil (6” deep), the mass of soil
microbes (biomass) is approximately equivalent to:
A. 1 sheep (150 lbs)
B. 1 cow (1,500 lbs)
C. 1 African elephant (10,000 lbs)
D. 3 African elephants (30,000 lbs)

9. Soil Science Society of America www.soils.org | www.soils4teachers.org
Soil is the most complex habitat on earth
and supports a HUGE number of organisms
(mostly microscopic)

10. Soil Science Society of America www.soils.org | www.soils4teachers.org
Macrofauna
Bacteria & Archaea
Viruses (bacteriophage)
ABUNDANCE
(#
per
gram
of
soil)
10
102
103
106
107
108
1010
105
104
Microfauna Mesofauna
Protists
Nematodes
0.1 µm 1.0 µm 10 µm 100 µm
1000 µm =
1 mm
10 mm =
1 cm
Microorganisms
Soil organisms are small,
numerous, and diverse!

12. • A method to isolate and
see small arthropods from
soil and litter
• Small organisms will move
away from the heat and
light and down the funnel
into the preservative
ACTIVITY: Berlese Funnel

13. Berlese funnels in the lab of Dr. Ernie Bernard, University of Tennessee

14. Tips
• Choose samples were you
expect lots of insects:
compost piles, rotting logs,
leaf litter
• May take several days to see
organisms
Berlese Funnels: Explore and Discuss
• Use a microscope to see the organisms
• Draw pictures of the organisms
• Discuss the size of the organisms
• Discuss their role in the ecosystem as shredders and predators

15. Soil microfauna
https://youtu.be/VuHznslr8aI

16. Big Idea 3
Soil organisms perform essential ecosystem
functions such as decomposition of organic
compounds, carbon and nutrient cycling, and
soil structuring
Soil Science Society of America www.soils.org | www.soils4teachers.org

17. No Soil, No Life!
Soil Science Society of America www.soils.org | www.soils4teachers.org
Not a new idea:
‘Essentially, all life depends upon the soil ...
There can be no life without soil and no soil
without life; they have evolved together.’
-Charles E. Kellogg, USDA Yearbook of
Agriculture, 1938.
In other words…
….life above ground depends on the life below
ground!

18. Soils are a living system… just like the human body
Soil property or service… …is kind of like the human…
Decomposition, nutrient cycling
Stability and structure
Moisture regulation and transport
Biodegradation of
pollutants and pesticides
Biodiversity and pathogen control
Symbiotic relationships with plants (e.g. N
fixers with legumes, mycorrhizae)
Word Bank:
Circulatory system Liver
Digestive system Immune system Social network
Skeletal system

19. Soil Aggregation and the Pore Network
• Large and stable aggregates create more
pore space
• Greater diversity of pore spaces = more
complex habitat (niche) space = greater
diversity of organisms
Microbes help stick soil particles together
• Gels and glues e.g. extracellular polysaccharides,
glomalin
• Hyphae

20. DEMOSTRATION: Soil Glue
Demonstrates that less
disturbed soil contains
more “soil glue” and are
held together better
Soil Glue: Explore and Discuss
• Compare a disturbed and undisturbed soil
• Compare samples from the same soil at
different depths
• Discuss which soil likely has more pore space
for organisms
• Discuss which soil would be more resistant to
erosion during rainstorms

21. Decomposition
• Organisms that eat dead plants and
animals (DETRITUS) are called
DECOMPOSERS
• Decomposers are an important part
of the food web:
o Make space
o Release nutrients
o Mix organic matter into soil
o Control the long term storage of
soil organic matter

22. Activity
https://youtu.be/akMT1ZZQ8PA

23. Soil Your Undies: Exploration
and Discussion
• Faster decomposition rate = more biological activity
• Test impacted vs. natural sites
• Topics for discussion
o Cotton vs. synthetic underwear
o Summer vs. winter decomposition
o Ways to support soil life
http://www.gatewaygreening.org/soil-
your-undies-lesson-by-rachel-wilson/

24. Put Your Results on the Map!
Soil Your Undies
Challenge Tracker

26. Soils4Teachers.org
• Investigate decomposition
with Tea4Science
• Explore soils under a
microscope
• Investigate how leaf litter
insulates the soil
…and more!

27. Other Media Resources on Soil Biology
Global Soil Biodiversity Atlas
(free pdf download)
https://www.globalsoilbiodiversity.o
rg/atlas-introduction
Life in the Soil Podcast
https://rilliglab.org/podcast/
Journey to the Microcosmos
YouTube Channel
https://www.youtube.com/c/mic
rocosmos