Download Soil Biology

 Upper
layer of soil (rooting zone) is
where ENERGY is present in soil
 This
is the LIVING SYSTEM of soil
 Incredible diversity
• Soil quality is dependent on species diversity
 The
means for energy to flow from sun to
all organisms.
Fourth-order consumer
Secondary consumer
heterotrophs
Tertiary consumer
Primary consumer
green plants;
photosynthetic
bacteria and algae
autotrophs
Primary Producer
AUTOTROPHS :
manufacture living (organic)
tissue from non-living (inorganic)
chemicals
HETEROTROPHS :
rely on autotrophs
Green plants, photosynthetic bacteria, algae
contain CHLOROPHYLL
• reflects green; absorbs all other colors
 absorption of light = absorption of energy
PHOTOSYNTHESIS:
CO2 + H2O + energy C6H12O6 + Oxygen
(sun)
Glucose:
carbohydrate
Only autotrophs can do this!
RESPIRATION
• Plants and animals derive energy
C6H12O6 +Oxygen  CO2 + H2O + energy
Heterotrophs do this.
Animals, roots, microorganisms in soil
Decomposition is a respiration process.

Gross primary productivity: rate at which
energy is stored in organic chemicals by
primary producers in photosynthesis.

In respiration, carbohydrates are broken
down and energy is released; remaining
carbohydrates can become plant tissue.

Net primary productivity: rate at which
energy is stored in plant tissue.

Gross P.P. = Respiration + Net P.P.
 Far
more important for energy flow
 Study
of yellow poplar forest:
• Of total energy fixed by forest:
 50% maintenance and respiration
 13% new tissue
 2% eaten by herbivores
 35% to detrital food chain
 Study
of grassland ecosystem:
• Energy stored:
 2/3 – ¾ returned to soil as dead plant material
 <1/4 consumed by herbivores
 ½ of that returned to soil as feces
 Eukaryotes
have cell membranes and
nuclei
• All species of large complex organisms are
eukaryotes, including animals, plants and fungi,
although most species of eukaryotic protists are
microorganisms.
 Prokaryotes
• bacteria
lack nucleus
 bacteria
 actinomycetes
 Abundant; most
important
decomposers with fungi
 Adaptable
 Specialized:
• Non-photosynthetic
• Photosynthetic
• Oxidize ammonium, nitrite, iron, manganese
• Oxidize sulfur
• Nitrogen-fixing
• Aerobic, anaerobic
 Single
cell division
• In lab: 1 can produce 5 billion in 12 hours
• In real world limited by predators, not enough
water, not enough food
 Abundant
in rhizosphere
• zone surrounding root
 dead root cells and exudate stimulates microbial
growth
1/10 inch
Exudates: carbohydrates and proteins secreted by roots
attracts bacteria, fungi, nematodes, protozoa
Bacteria and fungi are like little fertilizer bags
Nematodes and protozoa eat and excrete the fertilizer
 Organic
chemicals in big complex chains
and rings
• Bacteria break bonds using enzymes they
produce
 Create simpler, smaller chains
 Filamentous
 morphology
varies
 adaptable to drought
 neutral pH
 usually aerobic heterotrophs
 break down wide range of organic
compounds
Protozoa
Algae
Fungi
 Unicellular
 Amoeba, ciliates, flagellates
 Heterotrophic
• Eat bacteria, fungi
Form symbiotic relationships
e.g., flagellates in termite guts; digest
fibers
 Require
water
• Go dormant within cyst in dry conditions
 Filamentous, colonial, unicellular
 Photosynthetic
• Most in blue-green group, but also yellow•
•
•
•
•
green, diatoms, green algae
Need diffuse light in surface horizons;
important in early stages of succession
Form carbonic acid (weathering)
Add OM to soil; bind particles
Aeration
Some fix nitrogen
 Break
down OM, esp important where
bacteria are less active
 Most are aerobic heterotrophs
 chemosynthetic: adsorb
for energy
 branched
spores
 attack
dissolved nutrients
hyphae form mycelium: bears
any organic residue
 Mycorrhizae: symbiotic
absorbing
organisms infecting plant roots,
formed by some fungi
• normal feature of root systems, esp. trees
• increase nutrient availability in return for
energy supply
• plants native to an area have well-developed
relationship with mycorrhizal fungi
 Higher
fungi have basidium : club-shaped
structure , bearing fruiting body
• toadstools, mushrooms, puffballs, bracket fungi
(Macrofauna: > 1 cm long)
ANNELIDS
several types
CHORDATES (vertebrates)
mammals, amphibians, reptiles
PLATYHELMINTHES (flatworms)
ASCHELMINTHES (roundworms, nematodes)
MOLLUSKS (snails, slugs)
ARTHROPODS : (insects, crustaceans, arachnids,
myriapoda)
 Squirrels, mice, groundhogs, rabbits,
chipmunks, voles, moles, prairie dogs,
gophers, snakes, lizards, etc.
 Contribute
 Taxicabs
dung and carcasses
for microbes
 Nonsegmented, blind
>
roundworms
20,000 species
 Eat
bacteria or fungi or plants (stylet)
• And protozoa, other nematodes, algae
 Specialized
mouthparts
• Can sense temperature and chemical changes
 nematode
¾
of all living organisms
 Exoskeleton, jointed legs, segmented
body
 Insects
 Crustaceans
 Arachnids
 Myriapoda
 Shredders
 Microbial
taxis
Feeding Habits
Carnivores : parasites and predators
Phytophages: eat above ground green
plant parts, roots, woody parts
Saprophages: eat dead and decaying
OM
Microphytic feeders: eat spores,
hyphae, lichens, algae, bacteria
Movement
existing pore spaces,
excavate cavities,
transfer material to surface
improve drainage,
aeration,
structure,
fertility,
granulation
Distribution with depth
most active biotic horizons correspond
with amount of OM:
 Litter (O): has most OM but extremes of climate,
therefore only specialists live there
 Most animals in litter
Roots:
• Rhizosphere: zone surrounding root
 dead root cells and exudate stimulates microbial
growth
 Most microbiotic population in A and rhizosphere
Soil Organic Matter
and Decomposition
+O
Organic cmpd
2
(or other electron acceptors)
CO2 + H2O + energy + inorganic nutrients
a form of respiration.
an oxidation reaction
aided by microbial enzymes.
 Get
 Get
carbon from organic compounds
energy from aerobic respiration
 Use oxygen as electron acceptor in
decomposition
1. Anaerobic respiration
use nitrate, sulfate (or others) as electron
acceptor
2. Fermentation
use organic substrate as electron acceptor
(instead of oxygen)
 reduced to by-product, such as alcohol or
organic acid

 In
aerobes, when oxygen accepts
electrons, and is reduced, toxic
compounds (e.g., hydrogen peroxide)
are produced.
 Aerobic
organisms have adapted
mechanisms (2 enzymes) to counteract
toxins
 ANAEROBES
LACK THESE ENZYMES
• Nutrients, Carbon, Energy.
 Up to 50% of C in decomposed compounds is
retained as microbial tissue
 Some N,P,S also
 If amount of nutrients exceeds amount needed by
microbes, released as inorganic ions (NH4+, SO4-2,
HPO4-2)
organic
compounds
mineralization
immobilization
inorganic
compounds
 In
mineralization, nutrients formerly
stored in organic form are released for
use by living organisms
 In
immobilization, these nutrients are
reabsorbed and assimilated by living
organisms
1 rapid
to
6 slow
4
5
2
3
6
6
1
Friends don’t
let friends
eat humus.
 “Amorphous, colloidal
mixture of
complex organic substances, not
identifiable as tissue”.
 C:N:P:S = 100:10:1:1
 Composed of humic substances
• Resistant, complex polymers
 10s to 100s of years
 and nonhumic substances
• Less resistant, less complex
 Large
surface area per unit volume
• Greater than clay
 Negatively
charged
• OH- and COOH- groups
• High nutrient holding capacity (high CEC)
• High water-holding capacity
 Zymogenous: opportunists; eat “easy”
food; reproduce rapidly
 Autochthonous: eat
very resistant organic
compounds; slowly reproducing
Notice:
CO2 levels
Feeding frenzy
Priming effect
Arrows: C transfers
Humus levels
(p. 358)
 Decomposing
residue is not only a
source of energy, but also a source of
nutrients for microbial growth.
N
is the element most often lacking in
soil/residue to point of limiting microbial
population growth
 Limiting factor
 Carbon
usually makes up 45 – 55% of
dry weight of tissue
 Nitrogen can vary from < 0.5% >6.0%
For a residue with:
50% carbon and 0.5% N, C:N ratio would be
100:1 (wide/high C:N)
50% carbon and 3.0% N, C:N ratio would be
16:1 (narrow/low C:N)
?
?
 determines
rate at which residue will
decay and whether it will release
(mineralize) or immobilize N after
incorporation into soil.
Soil microbe cells need 8 parts C for 1
part N (C:N = 8:1)
only 1/3 of C from food is incorporated
into cells
therefore, they need food with a C:N of
?
24:1
 If
C:N ratio > 24:1, intense competition
among microbes for soil N
 Comparatively
low N
 Microbes suffer a shortage as they begin
decomposing, so have to get N from soil
at a cost in energy expenditure and
decomposition rate
 Greater energy expense and release of
CO2
 Higher proportion of C in resistant
compounds (cellulose, lignin)
 slower decomposition
 Sawdust
 Newspaper
 Wood
 Straw
chips
 Comparatively high N content
 Mineralized N will be released
decay starts
soon after
• So microbes won’t suffer a shortage as they
begin decomposing
 More
C from residue can be diverted to
microbial growth
 Higher proportion of total C in easily
decomposable compounds
 Faster decomposition
 Manure
 Cover
crop
 Household compost (composted)
1. Add high/wide
C:N residue:
microbial activity, CO2
long nitrate depression
final N level
2. low/narrow C:N:
microbial activity, CO2
no nitrate depression
final N level
(p. 361)