Transcript Soil Ecology

SOIL ORGANISMS
Global Soil Biodiversity
Initiative
 website
KINGDOMS OF LIFE
 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 lack nucleus
 bacteria
Organic portion composed of:
10%
5%
85%
Humus & decomposing
organic litter
Living Fresh
organisms residue
<5% <10%
Stabilized
organic
matter
(humus)
33% - 50%
Decomposing
organic matter
(active
fraction)
33% - 50%
The divisions of the 5%:
40% bacteria and actinomycetes
BACTERIA
 Bacterial biomass dominates :
 grassland and agricultural landscapes
Fungal biomass dominates:
Forests
bacteria
Bacteria
 Tiny (1 μm width), one-celled
 Single cell division
 In lab: 1 can produce 5 billion in 12 hours
 (In real world limited by predators, water & food availability)
 Abundant in rhizosphere
 Four FUNCTIONAL GROUPS:
 Decomposers
 Mutualists : partner with plants
 Pathogens
 Chemoautotrophs
Some terms:
 Autotrophs: can make organic compounds from inorganic
compounds
 Heterotrophs: feed on others to make organic compounds
 Chemosynthetic: get energy from inorganic chemical reactions
 Photosynthetic: get energy from sun
 Aerobes: use aerobic respiration (need oxygen as electron
acceptor)
 Anaerobes: use inorganic or organic compounds for electron
acceptor
Decomposers
 Organic chemicals in big complex chains and
rings
 Bacteria break bonds using enzymes they produce
 Create simpler, smaller chains
Mutualists
e.g., Nitrogen-fixing Bacteria
Nodules formed
where Rhizobium
bacteria infected
soybean roots.
Root nodules
Chemoautotrophs
 Get energy from OTHER THAN CARBON
compounds
 From N, S, Fe, H
Actinomycetes
 Are bacteria but grow
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like fungi
Filamentous but
morphology varies
Adaptable to drought
Important at high pH
Usually aerobic heterotrophs
Break down wide range of organic
compounds
Produce geosmin (smell of “fresh soil”)
40% other Microflora
Protozoa
Algae
Fungi
PROTOZOA
Ciliates • Largest of the three
• Move by means of hair-like cilia
• Eat other protozoa and bacteria
Amoeba
• Also large
• Move by means of a temporary foot (pseudopod)
Flagellates • Smallest of the three
• Move by means of a few whip-like flagella.
Protozoa
Flagellates
Amoeba
Ciliates
Eat bacteria &
protozoa
protozoa
 Unicellular
 Heterotrophic
 Eat bacteria, fungi
Form symbiotic relationships
e.g., flagellates in termite guts; digest
fibers
 Require water
 Go dormant within cyst in dry conditions
Function of protozoa
 Make nutrients plant-available
 Release excess N from the bacteria they eat
 Regulate bacteria populations
 Compete with pathogens
PROTOZOA
Sand
bacteria
protozoa
Flagellate
Ciliate
Amoeba
bacteria
amoeba
Soil-Dwelling “Vampires”
Vampyrellids
 Group of amoebe that drill holes in fungus and consume liquid
Archaea ( ar-KEY-ah)
 A recent discovery: 1970s
 Woese and Fox:
 Divided bacteria into “normal” and “extremophiles”
(archaeabacteria)
 Changed classic “tree of life”
Bacteria
Archaea
Eukaryotes
 Very similar to bacteria in shapes and size and
reproduction
 Differences:
 Cell membranes contain lipids
 Not chitin (like fungi)
 Not cellulose (like plants)
 Genes of archaea are more similar to eukaryotes
than to bacteria
 Can use a lot of various substances for energy
Importance
 Role in carbon cycle
 Photoautotrophs, chemoautotrophs,
photoheterotrophs, chemoheterotrophs
 Many can survive in extreme environments
(enzymes); heat, cold, salt, low pH
 Many are methane-producers:
 Swamp gas, cow farts
 Sheer numbers:
 Combined marine and soil archaea make them the
most abundant organism on earth
Importance in Soil
 Role in N cycle
 Ammonia oxidizers
 Decomposition
 Important anaerobic decomposers
 Important in extreme environments where
bacteria do not fluorish
algae
 Filamentous, colonial, unicellular
 Photosynthetic
 Most in blue-green group, but also yellow-green,
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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
Fungi
 Break down OM, esp important where
bacteria are less active
 attack any organic residue
 Most are aerobic heterotrophs
 chemosynthetic: adsorb dissolved nutrients
for energy
 Grow from spores into branched hyphae
 Hyphal strand divided into cells by septa that allow
flow of liquids between cells
Masses of hyphae grow together in visible threads
called mycelia
Advantages over bacteria:
 They can grow in length
 Rate: 40 μm / min (bacterium travels 6 μm in its life)
 Don’t need a film of water to move
 Can find new food sources
 Transport nutrients great distances
 Produce enzymes that break down complex
compounds
 Can break down lignin (woody compound that
binds cellulose), shells of insects, bones
 Can break down hard surfaces
Clever, clever adaptations!
 Infecting a nematode
 Hypha twists back on itself and catches a
nematode, hyphal cells swell and kill nematode
then enter body and suck out nutrients
 Oyster mushroom
 Emits toxic drops from hyphal tips which touch
nematode, immobilize it and hyphae enter body
and remove nutrients
 Trap arthropods or protozoa and digest them
 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
 Can extend the effective surface area of tree’s
roots by 700-1000 x
Mycorrhizae
Tree
root
Fungal
hyphae
Mycorrhizal
structure
Ectomycorrhizal
 Grow close to root surfaces
 Hardwoods and conifers
Endomycorrhizal
 Penetrate and grow inside
roots
 Vegetables, annuals,
grasses, shrubs, perennials,
softwoods
Ectomycorrhizae
Arbuscular Mycorrhizae (AM)
 Higher fungi have basidium : club-shaped
structure , bearing fruiting body
 toadstools, mushrooms, puffballs, bracket fungi
Fungi and Soil Quality
 Decompose carbon compounds
 Improve OM accumulation
 Retain nutrients in the soil
 Bind soil particles
 Food for the rest of the food web
 Mycorrhizal fungi
 Compete with plant pathogens
12% Earthworms
(Macrofauna: > 1 cm long)
ANNELIDS
earthworms
 Some 7000 species
 3 categories:
 Epigeic (leaf
litter/compost dwelling )
 Endogeic (topsoil or
subsoil dwelling )
 Anecic (deep burrow
drillers)
 Giant
 Benefits to soil
 Move air in and out of
soil
 Castings are rich in
available nutrients
 Produce 10 lbs / yr
 1 acre good garden soil: 2-3 million
 1 acre forest soil: 50,000
Other Macrofauna (5%) and
Mesofauna(3%)
CHORDATES (vertebrates)
mammals, amphibians, reptiles
PLATYHELMINTHES (flatworms)
ASCHELMINTHES (roundworms, nematodes)
MOLLUSKS (snails, slugs)
ARTHROPODS : (insects, crustaceans, arachnids, myriapoda)
vertebrates
 Squirrels, mice, groundhogs, rabbits,
chipmunks, voles, moles, prairie dogs,
gophers, snakes, lizards, etc.
 Contribute dung and carcasses
 Taxicabs for microbes
nematodes
NEMATODES
NEMATODES
Bacteria feeder
Fungal feeder
Predatory Nematode
Root-feeding nematodes
Nematode Trappers
Fungal hyphal rings constrict when a
nematode swims through.
 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
arthropods
 ¾ of all living organisms
 Exoskeleton, jointed legs, segmented body
 Insects
 Crustaceans
 Arachnids
 Myriapoda
 Shredders
 Microbial taxis
Mites
arachnids
Extracted from one ft2 of top two inches
of forest litter and soil
Springtails
 Arthropods
 Invertebrates with
external skeleton
 Spring or hop
 Detrivores
 100,000 / m3 topsoil
Beetles
Arthropods; order Coleoptera
400,000 species (40% of all
known insect species)
Some omnivores, some
eat plants, fungi, some
are carnivores
Larvae (grubs)
pseudoscorpons
 Arachnid
 Joint-legged
invertebrate
 Carnivorous: eat
larvae, ants, mites, flies
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
Rove beetles