Soil Ecology Flashcards
(60 cards)
1
Q
In a healthy soil one might find…
A
- Several species of vertebrate animals
- Several species of earthworms
- 20-30 species of mites
- 50-100 species of insects
- Dozens of species of nematodes
- Hundreds of species of fungi
- Thousands of species of bacteria and actinomycetes
2
Q
Abundance of Soil Organisms
A
Number Biomass1
Organism per gram soil (lbs per
(~1 tsp acre 6”)
Earthworms - 100 – 1,500
Mites 1-10 5 – 150
Nematodes 10 – 100 10 – 150
Protozoa up to 100 thousand 20 – 200
Algae up to 100 thousand 10 – 500
Fungi up to 1 million 1,000 – 15,000
Actinomycetes up to 100 million 400 – 5,000
Bacteria up to 1 billion 400 – 5,000
3
Q
Benefits of diversity
A
- Functional Diversity
- Functional Redundancy
- Ecosystem Stability
- Ecosystem Resilience
4
Q
Functional Diversity
Benefits of diversity
A
Capacity to utilize a wide variety of substrates and carry out a wide array of processes
5
Q
Functional Redundancy
Benefits of diversity
A
Multiple species capable of carrying out the same function
6
Q
Ecosystem Stability
Benefits of diversity
A
Soil has several ways to accomplish the same function (provided by functional redundancy)
7
Q
Ecosystem Resilience
Benefits of diversity
A
Soil has the ability to bounce back to functional health from a severe disturbance
8
Q
Soil organisms can be grouped on the basis of:
A
Soil organisms can be grouped on the basis of:
-Size:
Macro (>2 mm)
Meso (2 – 0.1 mm)
Micro (<0.1 mm)
- Taxonomy:
- Ecological Function:
9
Q
Primary producers
A
Autotrophic organisms
-Derive energy from sunlight used to fix (reduce C).
Ex: Plants, algae, lichens, bacteria
10
Q
Primary consumers
A
Herbivores and detritivores Bacteria, earthworms, nematodes, fungi
11
Q
Secondary consumers
A
Predators, parasites, carnivores Bacteria, fungi, protozoa, nematodes, mites, earthworms
12
Q
Higher level consumers
A
Predators
Mammals, birds, beetles, spiders, centipedes, mites
13
Q
Taxonomic groups and function
Macro-organisms
A
- Plants (and algae)
- Soil dwelling animals
14
Q
Taxonomic groups and function
Micro-organisms
A
- Fungi
- Bacteria (Monera)
- Actinomycetes
- Protozoa
15
Q
Plants (and algae)
Taxonomic groups and function
Macro-organisms
A
- Photosynthetic
- Primary producers
16
Q
Soil dwelling animals
Taxonomic groups and function
Macro-organisms
A
- Vertebrates: gophers, mice, voles, snakes
- Arthropods: spiders, ants, termites, beetles, maggots
- Annelids: earthworms
- Mollusks: snails, slugs
- Helminths (non-segmented worms): nematodes
17
Q
Fungi
Taxonomic groups and function
Micro-organisms
A
- Largest biomass in most soils
- Yeasts, molds, and mushrooms
18
Q
Bacteria (Monera)
Taxonomic groups and function
Micro-organisms
A
- Extremely diverse
- Single celled, small, 0.5 – 5 µm
19
Q
Actinomycetes
Taxonomic groups and function
Micro-organisms
A
- (filamentous bacteria)
- Genetically related to bacteria
- Functionally similar to fungi
20
Q
Protozoa
Taxonomic groups and function
Micro-organisms
A
- Single celled, mobile,
- Larger than bacteria 6 – 100 µm
21
Q
Higher plants are the primary source of organic material added to soil
Plant roots
A
- In grasslands 50 – 60% of total plant biomass is below ground
- In forests 40 – 70% of plant production is in the root systems
- Arable crops root mass is normally about 15– 40% of the above ground crop mass
- Crops add from 2500 to 8500 kg/ha of root residue to soil
22
Q
Soil physical modifications
Plant roots
A
- Roots expand into soil cracks, then expand
- Encourage soil shrinkage and cracking, stabilizes soil aggregates
- Root exudates support microbial growth
23
Q
The Rhizosphere
A
- The zone of soil that is significantly influenced by living roots
- Extends out from the root surface
- The rhizosphere is enriched in organic material
- Microbial activity in the rhizosphere is greater than in the bulk soil.
24
Q
Soil Algae
A
- Algae contain chlorophyll
- Like the higher plants, algae are primary producers
- Most soil algae live near or at the soil surface
- Cyanobacteria (blue-green algae) often form associations with fungi to form lichens and microbiotic crusts in desert regions
25
Soil Dwelling Animals
```
Vertebrates:
Arthropods:
Annelids:
Mollusks:
Helminths:
```
26
Ecosystem Engineers
- Some soil-dwelling organisms make significant physical alterations to their environment that have significant influences on the soil ecosystem
- Burrowing animals such as earthworms, ants, termites, gophers, prairie dogs moles, rats
- Dung beetles bury feces of grazing animals, stimulate nutrient cycling, prevents reproduction of carnivorous flies
27
Earthworm effects on soil properties
- Burrows. Ingest 50 – 1000 Mg soil/ha/yr
- Casts/middens/burrow linings. Enhance aggregate formation and stability, improves soil physical properties
- Soil Nutrients. Physically grind up plant material, mix with soil, stimulate microbial decomposition
28
Ants and termites
- Tunneling and nesting activities of ants can improve soil aeration
- Ants may be herbivores, detritivores, or predators. Feeding activity breaks up organic material.
- Termites are major contributors to breakdown of organic matter at the soil surface.
- Many termites fungi “farmers”
- Termite mound building moves 300 – 1200 kg/ha/yr of soil. Brings subsoil material to surface.
- Termites tend to concentrate activity in mound area.
29
Nematodes
- Unsegmented roundworms found in almost all soils.
- 4 – 100 μm in cross section, up to several mm long
- Most nematodes are predators on other nematodes, bacteria, fungi, algae, protozoa, and insect larvae.
- Bacterial grazing by nematodes releases large amounts of N to soil because bacteria contain more N than nematodes can assimilate.
- Some nematodes are plant parasites. They pierce root cells with their mouth parts. The wound allows infection of the plant by secondary pathogens.
30
Protozoa
- Most abundant and varied microfauna in soil, but often classified as Protista rather than animals
- Size range 6 – 100 µm diameter
- Mobile, single celled organisms that capture and engulf their food
- Many waterborne protists cause serious human diseases (most soilborne protists do not)
- Most soil borne protozoa prey on bacteria and control their populations
- Significant in release of nutrients consumed by bacteria
31
Fungi
-Extremely diverse group of microorganisms
10,000s of species from 170 genra
-May be up to 1,000,000 still to be discovered in soil
-Numbers in soil usually less than bacteria but because of larger size they often make up the bulk of microbial biomass in soil
Include Yeasts, Molds and Mushrooms
32
Yeasts
| Group of Fungi
- Single celled
| - Anaerobic
33
Molds
| Group of Fungi
- Filamentous
- Important in organic matter breakdown
- Some favored at low pH
34
Mushrooms
| Group of Fungi
- Fruiting structures are visible,
- Edible mushrooms important industry and hobby
- Important in breakdown of woody tissue.
- Some form mycorrhizae
35
Fungi
| Continued
- Most versatile and persistent decomposers of any group of soil organisms
- Capable of degrading more complex organic molecules such as cellulose, lignin, gums
- Important in nutrient cycling, humus formation and aggregate stabilization
- More efficient than bacteria, they assimilate into their tissues up to 50% of the material they decompose (~20% for bacteria)
- Synthesize a wide range of organic compounds
- Some are beneficial, such as penicillin and other antibiotics
- Some are toxic (mycotoxins, aflatoxins
- Some fungi are plant pathogens (Verticillium, Rhizoctonia)
- Some potential for use of fungi as biocontrol agents against insects and mites
36
Bacteria size and shape
- Very small (0.5 – 5 µm), single-celled, prokaryotic (no distinct nucleus), may be
- Round (coccus)
- Rodlike (bacillus)
- Spiral (spirillum)
37
Bacteria
| Characteristics
- Most diverse group of soil organisms, able to survive in extreme environments (pH, temperature, redox)
- Very rapid reproductive potential (a few hours to regenerate)
- May be autotrophic (photo- and chemo-) or heterotrophic (most).
- Early decomposers, predominate on easily decomposed substrates
- Most decomposition in anaerobic environments is bacterial
38
Bacteria's responsibility
-Bacteria possess of a very broad range of enzymatic capabilities
bacteria are a “bag of enzymes”
-Responsible for numerous enzyme mediated chemical transformations in soil
-Nitrogen transformations
-Oxidation/reduction reactions (S, Fe, Mn, C)
-Decomposition of organic molecules
-Also capable of degrading a wide range of xenobiotic chemicals, used extensively for remediation of polluted soil
-Hydrocarbons (diesel fuel, gasoline, crude oil)
-Pesticides
-Solvents
-Explosives
-Though lower biomass/area than fungi, high surface to volume ratio (and rapid regeneration) makes them very “reactive”
~70 ha of bacterial surface area per ha of soil
39
Actinomycetes
- Filamentous and highly branched like fungi, but mycelial threads are smaller
- Part of the bacterial domain in that they are prokaryotic, unicellular, about the same diameter
- Almost all are aerobic heterotrophs
- Many species produce antibiotics (actinomycin, neomycin, streptomycin)
- A few are capable of N fixation
- Especially numerous in soils with high humus content
- Capable of decomposing more resistant organic compounds such as cellulose, phospholipids, lignin and chitin
- Release a class of compounds known as “geosmins” responsible for the earthy aroma of freshly turned soil
40
Interactions of soil organisms
- Commensalist – live side by side with little interaction
- Parasitic – one organism lives at the expense of another
- Symbiotic – mutually beneficial relationship
41
Organic matter decomposition
| Everyone is involved
- Earthworms
- Soil insects and other arthropods
- Bacteria
- Fungi
- Actinomycetes
- Protists and nematodes, the predators
42
Earthworms
Organic matter decomposition
Everyone is involved
- Mix fresh organic materials into the soil
| - Brings organic matter into contact with soil microorganisms
43
Soil insects and other arthropods
Organic matter decomposition
Everyone is involved
- Shred fresh organic material into much smaller particles
| - Allows soil microbes to access all parts of the organic residue
44
Bacteria
Organic matter decomposition
Everyone is involved
Population increases rapidly when organic matter is added to soil
- Quickly degrade simple compounds - sugars, proteins, amino acids
- Have a harder time degrading cellulose, lignin, starch
- Cannot get at easily degradable molecules that are protected
45
Fungi
Organic matter decomposition
Everyone is involved
- Grow more slowly and efficiently than bacteria when organic matter is added to soil
- Able to degrade complex organic molecules such as cellulose, lignin, starch
- Give other soil microorganisms access to simpler molecules that were protected by cellulose or lignin
46
Actinomycetes
Organic matter decomposition
Everyone is involved
- The cleanup crew
- Become dominant in the final stages of decomposition
- Attack the highly complex and decay resistant compounds
- Cellulose
- Chitin (insect shells)
- Lignin
47
Protists and nematodes, the predators
Organic matter decomposition
Everyone is involved
- Feed on the primary decomposers (bacteria, fungi, actinomycetes)
- Release nutrients (nitrogen) contained in the bodies of the primary decomposers
48
Organic matter decomposition
| Carbon and Nitrogen Cycling
- During each cycle of degradation about 2/3 of the organic carbon is used for energy and released as carbon dioxide (CO2)
- During each cycle of degradation about 1/3 of the organic carbon is used to build microbial cells or becomes part of the soil organic matter
49
Organic matter decomposition
Carbon and Nitrogen Cycling
C/N 24:1
(Litter C/N ratio around 24:1)
- -> (C/N ratio 8:1)
- ->Average C/N ratio of bacteria and fungi is 8:1 ((Microbial C/N ratio is maintained at 8:1 with no uptake or release of N))
- -> (CO2) 2/3 of carbon released as CO2
50
Organic matter decomposition Carbon and Nitrogen Cycling
| C/N: 90:1
(Litter C/N ratio around 90:1)
- ->C/N ratio 30:1
- ->Average C/N ratio of bacteria and fungi is 8:1 (CO2) 2/3 of carbon released as CO2
-Immobilization
51
Organic matter decomposition Carbon and Nitrogen Cycling
| C/N 9:1
(Litter C/N ratio around 9:1)
- ->C/N ratio 3:1
- ->Average C/N ratio of bacteria and fungi is 8:1 (Microbial C/N ratio is maintained at 8:1 by releasing N to the soil)
- ->Soil N
- ->CO2 (2/3 of carbon released as CO2)
- Mineralization
52
Symbiotic Nitrogen Fixation
- Many bacteria have the ability to “fix” or convert atmospheric nitrogen into forms that plants can utilize.
- Some of these bacteria, notably the rhizobia species, form symbiotic relationships with leguminous plants
- The plants provide Rhizobia with a steady source of food (sugars)
- The rhizobia provides the plant with nitrate nitrogen
- Efficiency nitrogen fixation is greatly increased by this relationship
53
Mycorrhizal fungi
| Plant/fungi symbiosis
- Mycorrhizae means “fungus root”
- Fungi live in close association with plant roots
- May live on the external surface of roots (ectomycorrhizal)
- Fungal hyphae may invade root cells (endomycorrhizal)
VAM fungi growing in symbiotic association with a plant root.
- Root cells
- Fungal hyphae
- Vesicles – food storage
- Arbuscule – exchanges nutrients with plant
54
Mycorrhizal fungi
| Plant/fungi symbiosis
- Plants supply fungi with sugars (energy)
- Fungal hyphae grow 5 – 10 cm beyond plant roots
- Extend to soil pores too large for root hairs
- Increase plant nutrient supply, especially phosphorus
- Increase plant water supply
55
Soil factors that affect microorganism growth
- Organic matter
- Aeration
- Moisture and temperature
- Soil fertility and pH
56
Organic matter
Soil factors that affect microorganism growth
(they need to eat) – source of energy
57
Aeration
Soil factors that affect microorganism growth
(oxygen, they need to breathe) – most soil microbes are aerobic, some are anaerobic (some bacteria)
58
Moisture and temperature
Soil factors that affect microorganism growth
(they need to be comfortable) – optimum moisture usually in the range of -10 to -70 kPa, optimum temperature in the range 20 - 40°C
59
Soil fertility and pH
Soil factors that affect microorganism growth
(they need nutrients) – high Ca availability and near neutral pH most favorable to the broadest range of soil microbes
60
Effects of soil management practices on soil organisms
- Vegetative cover
- Soil disturbance (tillage)
- Soil pH and fertility
- Soil mulch and organic matter additions
- Pesticide applications
