Who lives in
the soil ??
The Furrow
Soil is an
archive of life
on earth!
Quantifying Biodiversity
Group
Known
Species
Estimated
Total
Species
Percentage
Known
Vascular
plants
220,000
270,000
81%
Algae
40,000
60,000
67%
Fungi
69,000
1,500,000
5%
3,000
30,000
10%
Bacteria
Most occur in soil
(Hawksworth, 1991)
Most are tiny !!!
Soil organisms vary widely in size
Body size
increasing
Abundance

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

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





Viruses
Bacteria
Fungi
Microflora
Algae
Protozoa
Microfauna
Nematodes
Microarthropods
Mesofauna
Enchytraeids
Earthworms
Macrofauna
Ants, termites, spiders
Mollusks
Megafauna
Others: rodents, snakes,
voles, amphibians, etc.
Body sizes and shapes are adaptations to
the many different spatial niches in soil
BACTERIA
cocci
have many different shapes
bacillus
spirilla
filamentou
s
SSS
A
Typically > 10 billion bacteria
per gram of soil
What do bacteria do in soil ?
 Colonize aerobic and anaerobic
environments
 Decompose labile substrates
 Mediate redox transformations
 Nourish bacterivores
 Fix N
N-fixing nodules
on a cowpea plant
Legume
love
affair
Sarrantonio
FUNGI
have many
different life
forms
–
–
–
–
Yeasts
Mycelia
Fruiting bodies
Spores
What do fungi do in soil ?
 Decompose recalcitrant organic
compounds
 Penetrate residues
 Stabilize soil structure
 Nourish fungivores
 Form symbioses with plant roots and soil
fauna
 Compete with plant pathogens
 Parasitize plants and soil animals
 Produce toxins e.g. aflatoxin produced by
Aspergillus flavus on peanut
Mycorrhizal diversity
Ectomycorrhizae
AM endomycorrhizae
Arbutoid
mycorrhizae
Ericoid
endomycorrhizae
Orchid endomycorrhizae
Lavelle and Spain (2001)
Mycorrhizal Networks: Connecting
plants intra- and interspecifically
•Many plants are
connected
underground by
mycorrhizal hyphal
interconnections.
•Mycorrhizal (AM)
fungi are not host
specific.
Illustration by Mark Brundrett
Increase nutrient (P) uptake
suppress pathogens
Mediate plant competition
Improve soil structure
Glomalin
Superglue
of the soil ??
PROTOZOA
Ciliates
•
•
Largest of the protozoa
Move by means of hair-like cilia
Amoebae
•
•
Also large
Move by means of a temporary foot
(pseudopod)
Include testate amoebae (with shell-like
covering), and naked amoebae
•
Flagellates
•
•
Smallest of the protozoa
Move by means of flagella (1-2)
Important bacterivores
Soil-Dwelling “Vampires”
Vampyrellid amoebae attacking Gaeumannomyces
graminis, the fungus that causes “take-all disease” in wheat.
NEMATODES
 Most abundant of the
soil fauna
 Functionally diverse
Bacterivores
Fungivores
Herbivores
Predators
Omnivores
 Most are beneficial promoting
decomposition
and nutrient recycling
http://nematode.unl.edu/hdigonic.htm
Nematode diversity
Bacterivore
Fungivore
Plant parasitic
Predatory
Galled root system of tomato infected with root-knot
nematode, Meloidogyne sp., compared with noninfected root system
Root knot juvenile penetrating a tomato root
http://www.agnr.umd.edu/users/nrsl/entm/nematology/images/eis143.jpg
Arthropods
exoskeleton
segmented body
jointed legs
Arthropod
diversity
Litter Shredders
Fungivores
Predators
Herbivores
Microarthropods
EARTHWORMS
anecic
~ 35 species
of earthworms
have been
found in
Illinois soils
~ half are exotic species from Europe and Asia
endogeic
epigeic
A new earthworm parasite has arrived in IL
After earthworms invaded
Before earthworms invaded
A new earthworm predator has arrived in IL
The geographic distribution of Bipalium adventitium in Illinois is unknown. Home
gardeners and nursery workers may see these exotic land planarians under
boards and stones or crawling on the soil surface after rains. They are up to 2.5
inches long and 1/8 of an inch wide when crawling. They are pale brown or tan
with a thin dark brown line running down their back. Scientists would appreciate
receiving reports of any observations of these creatures.
Contact Ed Zaborski at (217) 265-0330, or zaborski@uiuc.edu by e-mail
Epigeic species can be
used for vermicomposting
Earthworm cocoons
http://soils.usda.gov/sqi/soil_quality/soil_biology/images/CE8a-cocoon_LR_small.jpg
How do earthworms move through soil ?
Loose soil
They insert their anterior tip into a pore, extend their
setae to anchor most of their body and then exert
radial and longitudinal pressure. A cycle of
alternating contractions and relaxations thrusts their
body forward.
Dense soil
They invert their pharynx, exude lubricating mucus
and suck obstructive soil into their body.
How do earthworms eat ?
 Earthworms eat by pulling food into their mouth with
their prostomium (mouth) and pharynx which creates a
very strong suction.
 The food is stored in the crop and then ground up into
small digestible pieces in the gizzard.
 Earthworms need a gizzard because they do not have
any teeth. Nutrients are absorbed in the small intestine.
Where are the soil
organisms ??
Soil
organisms
are
concentrated
in
HOT
SPOTS !
drilosphere
detritusphere
porosphere
aggregatusphere
rhizosphere
Adapted from Coleman et al. (19??)
middens
casts
Drilosphere
Zone of
earthworm
influence
Which burrows were made by an endogeic ?
Capowiez et al. 2003)
In 1881, Darwin reported that healthy earthworms
sometimes leave their burrows at night and embark on a
“voyage of discovery”
Surface migration is a routine activity aimed at dispersal
and finding a mate. Surface migration usually occurs
during cloudy moist conditions. Both anecic and endogeic
earthworms are active surface migrants.
Rhizosphere
< 10 % of soil volume
Zone of root
influence
Navigating the rhizosphere
Rhizoplane
EndoRhizosphere
End of the rhizosphere
Ecto-Rhizosphere
< 10% of soil
volume
Root free soil
> 90%
of soil
volume
(Lavelle and Spain, 2001)
Detritusphere
surface residue
zone
Structural
rigidity
Tortuous, loosely
connected and highly
constricted porosity
The soil matrix presents
its inhabitants with
many challenges
Moisture
fluctuations
Low quality
nutritional
resources
Microorganisms have very limited ability to
move within the soil matrix.
As a result,
most
soil
microorganisms
are
For their prince charmings
in a dormant state
to arrive !
waiting…
Rain
Roots
There are many types of
prince charmings
Organic
amendments
Tillage
Soil fauna have a
disproportionate impact
on nutrient cycling,
energy fluxes and plant
growth
>90%
metabolic
activity
Soil fauna are relatively mobile
but have limited digestive ability
3 main types of digestive interactions
occur between soil fauna and microflora
Soil microflora are relatively immobile
but have almost unlimited
digestive ability
Microbivory
NH4
NH4+
+
NH4+
NH4+
NH4+
NH4+
Microfauna (e.g. protozoa and nematodes)
harness the microflora’s digestive abilities
by grazing on them
I want some
bacteria for
lunch !
External rumen digestion
The fecal pellets
many mesofauna
contain
Reingestion
of fecalofpellets
after a few days
of
shredded,
moistened
mixed but
largely
microbial
activity
greatlyand
increases
assimilation
undigested residues
Rumen digestion greatly
Soil macrofauna
areof
enhances
utilization
ecosystem
engineers
complex
substrates
by
soil macrofauna
Impact of
tillage on the
soil food web
Adapted from Hunt et al. (1986)
Soil organic matter fuels
the soil food web
Active OM
energizes
biologically
mediated
processes
SOM is a complex mixture
Biologically
active
SOM
Living organisms
Recent residues
Recalcitrant
SOM
HUMUS
Adapted from Magdoff and Weil (2003)