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Microbial Ecology (BIOL 355) > Lecture 4: Soil > Flashcards

Lecture 4: Soil Flashcards

1
Q

List the 3 types of microbial habitats.

A
  1. Air
  2. Aquatic
  3. Terrestrial
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2
Q

What are the types of aquatic habitats?

A
  • Freshwater
  • Marine
  • Brackish
  • Hypersaline
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3
Q

What are the types of terrestrial habitats?

A
  • Hard rock
  • Soil
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4
Q

Which of the following habitats has the most diverse communities of microbes?

A. Soils/sediments
B. Freshwater
C. Seawater
D. Atmostphere
E. Deep subsurface

A

A. Soils/sediments
B. Freshwater - stable
C. Seawater - nutrient poor
D. Atmostphere - nutrient poor?
E. Deep subsurface - stable

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5
Q

What does allochthonous mean?

A

Foreign

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6
Q

What does autochthonous mean?

A

Local

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7
Q

What are the stresses of rock surfaces as a habitat?

A
  • Desiccation
  • Low water potential
  • High UV
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8
Q

What types of organisms live on rock surfaces?

A
  • Cyanobacteria
  • Lichens (fungi and algae)
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9
Q

What are hypoliths?

A

Microbial communities that live on the underside of rocks or at the rock-soil surface

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10
Q

What are endoliths?

A

Microorganisms that live inside rocks or in pores between mineral grains

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11
Q

List and describe the 3 types of endoliths.

A
  1. Cryptoendoliths: live in rock on Earth’s crust
  2. Subsurface endoliths: found in groundwater aquifers or caves
  3. Deep-biosphere endoliths: found in deep, extremely hot or cold rock, miles beneath the ocean floor
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12
Q

Pseudomonas aeruginosa is a common bacteria found in _____.

A

soil

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13
Q

What does P. aeruginosa do?

A
  • Breaks up the toxic compounds that are a major concern of oil spills
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14
Q

Soil is a _____ medium.

A

porous

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15
Q

What is the composition of soil in terms of solids vs. pore space?

A

50/50

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16
Q

What is in the solid portion of soil?

A
  • Minerals
  • Organics only
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17
Q

What is in the pore space portion of soil?

A
  • Liquids (water)
  • Gases (air)
  • Flooding can reduce gas content
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18
Q

Soil has 3 “horizons”. List and describe each.

A
  1. A horizon
    - Topsoil: minerals, humus
  2. B horizon
    - Less broken down
  3. C horizon
    - Solid or partially broken-down rock
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19
Q

How do soil particles form?

A

By the breakdown of parent rock by weathering

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20
Q

List and describe the 2 types of refractory compounds.

A
  • Humic substances: decayed organic monomers that polymerize into complex molecules
  • Lignin: vegetation above affects soil type
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21
Q

List the 3 soil texture types from biggest to smallest particle size.

A
  1. Sand
  2. Silt
  3. Clay
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22
Q

_____ is the most fertile soil type.

A

Loam

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23
Q

Why is loam so fertile?

A

It has a good balance of clay, silt, and sand

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24
Q

Why are sand and clay not good for plant growth?

A
  • Sand won’t retain enough water
  • Clay retains too much water
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25
Q

Define humus.

A

Decayed organic matter

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26
Q

How does humus form?

A

Plant and animal matter decompose

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27
Q

How is humus important for plant nutrition?

A

Contains lots of nutrients form the decaying organic matter

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28
Q

What is topsoil composed of?

A

Inorganics

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29
Q

Most soil particles are negative aka _____.

A

anions

30
Q

Plant soil nutrients (NO3-, H2PO4-, SO42-) are also _____.

A

anions

31
Q

_____ attached to _____ soil particles.

A
  1. Cations
  2. negative
32
Q

What does soil pH affect?

A

The solubility of chemicals in soil (ionization)

33
Q

What affects soil pH?

A

Rainfall
- Leaches basic cations and promotes high organics –> acidic (low pH)
- Low rainfall –> higher pH –> neutral or alkaline

34
Q

What are the 3 general categories of soil fauna?

A
  1. Macro and megafauna
  2. Mesofauna
  3. Microfiora and microfauna
35
Q

What are soil animals (macro and megafauna) important for?

A
  1. Decomposition (shredding tissues)
  2. Mixing soil (aeration)
36
Q

List some examples of soil animals (macro and megafauna).

A
  • Termites
  • Pseudoscorpions
  • Earthworms
  • Centipedes
  • Snails
  • Voles
37
Q

What are soil mesofauna imporant for?

A
  1. Decomposition
  2. Predation
38
Q

List some examples of soil mesofauna.

A
  • Nematodes
  • Rotifers
  • Tardigrade
  • Springtails
39
Q

Describe soil microbes.

A
  • Most diverse group
  • Mostly bacteria
  • Exopolysaccharides involved in soil aggregation
  • 80-90% are sorbed onto particles
40
Q

Describe the type of bacteria found in soil.

A
  • Small
  • Mostly gram-negative
  • But above average % of gram-positive spore formers
40
Q

What type of archaea are found in soil?

A
  • Crenarchaeota
  • Thaumarchaeota
41
Q

Describe the type of fungi found in soil.

A
  • Less per gram than bacteria, but can compose more biomass
  • Saprophytes: decompose plant matter
  • Mycorrhizae: mutualistic association with plants
42
Q

What types of protists are found in soil?

A
  • Protozoa
  • Algae
43
Q

What is a slime mold?

A

A single-celled amoeboid-like protist

44
Q

_____ obtain carbon from producers passively from dead biomass, excretions and secretions.

A

Saprotrophs

45
Q

_____ and _____ obtain carbon from producers actively.

A
  1. Necrotrophs
  2. Biotrophs
46
Q

Necrotrophs actively obtain carbon by _____.

A

attacking and decaying biomass

47
Q

Biotrophs actively obtain carbon _____.

A

from plants in exchange for a microbe-supplied nutrient

48
Q

Explain the agricultural implications of soil microbes.

A
  • Role of microbes in decomposition and nutrient cycling is very important in soil
  • Humus generation
  • Nitrogen cycle (N fixation and denitrification)
49
Q

Nitrogen fixation converts _____ to _____.

A

N2 –> NH3

50
Q

Denitrification converts _____ to _____.

A

NO3 –> N2

51
Q

Define rhizobacteria.

A

Root-associated bacteria

52
Q

Define rhizosphere.

A

Thin layer of soil closely surrounding the plant’s roots

53
Q

What types of effect(s) do rhizobacteria have on the plant?

A

Can be detrimental, neutral, or beneficial

54
Q

Rhizobacteria can be _____ (free-living) or _____ (living between cells of the plant itself).

A
  1. Free-living
  2. Endophytic
55
Q

Both depend on nutrients secreted by plant cells and, in return, help to enhance plant growth by _____, _____, and _____.

A
  1. producing chemicals that stimulate plant growth
  2. producing antibiotics that protect roots
  3. increasing nutrient availability
56
Q

What element is often the limiting factor?

A

Nitrogen

57
Q

In what forms can plants absorb nitrogen? What form of nitrogen can they NOT use?

A
  1. Nitrate (NO3) and ammonium (NH4+
  2. Atmospheric nitrogen (N2)
58
Q

Nitrogen is needed for the synthesis of _____ that produce _____ and _____ that produce _____.

A
  1. Amino acids
  3. Nucleic acids
    4.
59
Q

Soil nitrate is formed through a 2-step process called _____.

A

nitrification

60
Q

What is the order of nitrification (i.e. what gets converted to what)?

A

ammonia –> nitrite –> nitrate

61
Q

What are the steps of acquiring soil ammonium (NH4+)?

A
  1. Nitrogen fixation: nitrogen-fixing bacteria convert atmospheric nitrogen to ammonia
  2. Ammonia can pick up an H+ in the soil solution and forms ammonium
62
Q

What enzyme facilitates nitrogen fixation?

A

Nitrogenase

63
Q

What do the plant and fungi provide for each other?

A
  • Plant provides sugars
  • Fungi provide more surface area (get water and minerals)
64
Q

What are the 2 major types of mycorrhizae?

A
  1. Ectomycorrhizae
  2. Arbuscular micorrhizae
65
Q

Which of the following habitats has the greatest abundance of microbes?

A. Soils/sediments
B. Freshwater
C. Seawater
D. Atmosphere
E. Deep subsurface

A

A. Soils/sediments
B. Freshwater
C. Seawater
D. Atmosphere
E. Deep subsurface

66
Q

Describe deep subsurface environments.

A
  • Huge area: large total global biomass possibilities
  • Fissures are important for water
67
Q

What are the implications of deep subsurface environments?

A

Possible early Earth evolution
- Protects from bombardment

68
Q

List the types of studies in deep drilling operations. What are the concerns for these?

A
  • Waste disposal
  • Gold mines
  • Seafloor drilling projects
  • Concerns: contamination (use rigorous sterile sampling processes)
69
Q

Describe the types of microbes in deep subsurface environments.

A
  • Diverse: autotrophic and heterotrophic pathways
  • Anaerobic and aerobic respiration

Microbial Ecology (BIOL 355) (17 decks)

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