Lecture 4: Soil Flashcards
1
Q
List the 3 types of microbial habitats.
A
- Air
- Aquatic
- Terrestrial
2
Q
What are the types of aquatic habitats?
A
- Freshwater
- Marine
- Brackish
- Hypersaline
3
Q
What are the types of terrestrial habitats?
A
- Hard rock
- Soil
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
5
Q
What does allochthonous mean?
A
Foreign
6
Q
What does autochthonous mean?
A
Local
7
Q
What are the stresses of rock surfaces as a habitat?
A
- Desiccation
- Low water potential
- High UV
8
Q
What types of organisms live on rock surfaces?
A
- Cyanobacteria
- Lichens (fungi and algae)
9
Q
What are hypoliths?
A
Microbial communities that live on the underside of rocks or at the rock-soil surface
10
Q
What are endoliths?
A
Microorganisms that live inside rocks or in pores between mineral grains
11
Q
List and describe the 3 types of endoliths.
A
- Cryptoendoliths: live in rock on Earth’s crust
- Subsurface endoliths: found in groundwater aquifers or caves
- Deep-biosphere endoliths: found in deep, extremely hot or cold rock, miles beneath the ocean floor
12
Q
Pseudomonas aeruginosa is a common bacteria found in _____.
A
soil
13
Q
What does P. aeruginosa do?
A
- Breaks up the toxic compounds that are a major concern of oil spills
14
Q
Soil is a _____ medium.
A
porous
15
Q
What is the composition of soil in terms of solids vs. pore space?
A
50/50
16
Q
What is in the solid portion of soil?
A
- Minerals
- Organics only
17
Q
What is in the pore space portion of soil?
A
- Liquids (water)
- Gases (air)
- Flooding can reduce gas content
18
Q
Soil has 3 “horizons”. List and describe each.
A
- A horizon
- Topsoil: minerals, humus - B horizon
- Less broken down - C horizon
- Solid or partially broken-down rock
19
Q
How do soil particles form?
A
By the breakdown of parent rock by weathering
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
21
Q
List the 3 soil texture types from biggest to smallest particle size.
A
- Sand
- Silt
- Clay
22
Q
_____ is the most fertile soil type.
A
Loam
23
Q
Why is loam so fertile?
A
It has a good balance of clay, silt, and sand
24
Q
Why are sand and clay not good for plant growth?
A
- Sand won’t retain enough water
- Clay retains too much water
25
Define humus.
Decayed organic matter
26
How does humus form?
Plant and animal matter decompose
27
How is humus important for plant nutrition?
Contains lots of nutrients form the decaying organic matter
28
What is topsoil composed of?
Inorganics
29
Most soil particles are negative aka _____.
anions
30
Plant soil nutrients (NO3-, H2PO4-, SO42-) are also _____.
anions
31
_____ attached to _____ soil particles.
1. Cations
2. negative
32
What does soil pH affect?
The solubility of chemicals in soil (ionization)
33
What affects soil pH?
Rainfall
- Leaches basic cations and promotes high organics --> acidic (low pH)
- Low rainfall --> higher pH --> neutral or alkaline
34
What are the 3 general categories of soil fauna?
1. Macro and megafauna
2. Mesofauna
3. Microfiora and microfauna
35
What are soil animals (macro and megafauna) important for?
1. Decomposition (shredding tissues)
2. Mixing soil (aeration)
36
List some examples of soil animals (macro and megafauna).
- Termites
- Pseudoscorpions
- Earthworms
- Centipedes
- Snails
- Voles
37
What are soil mesofauna imporant for?
1. Decomposition
2. Predation
38
List some examples of soil mesofauna.
- Nematodes
- Rotifers
- Tardigrade
- Springtails
39
Describe soil microbes.
- Most diverse group
- Mostly bacteria
- Exopolysaccharides involved in soil aggregation
- 80-90% are sorbed onto particles
40
Describe the type of bacteria found in soil.
- Small
- Mostly gram-negative
- But above average % of gram-positive spore formers
40
What type of archaea are found in soil?
- Crenarchaeota
- Thaumarchaeota
41
Describe the type of fungi found in soil.
- Less per gram than bacteria, but can compose more biomass
- Saprophytes: decompose plant matter
- Mycorrhizae: mutualistic association with plants
42
What types of protists are found in soil?
- Protozoa
- Algae
43
What is a slime mold?
A single-celled amoeboid-like protist
44
_____ obtain carbon from producers passively from dead biomass, excretions and secretions.
Saprotrophs
45
_____ and _____ obtain carbon from producers actively.
1. Necrotrophs
2. Biotrophs
46
Necrotrophs actively obtain carbon by _____.
attacking and decaying biomass
47
Biotrophs actively obtain carbon _____.
from plants in exchange for a microbe-supplied nutrient
48
Explain the agricultural implications of soil microbes.
- Role of microbes in decomposition and nutrient cycling is very important in soil
- Humus generation
- Nitrogen cycle (N fixation and denitrification)
49
Nitrogen fixation converts _____ to _____.
N2 --> NH3
50
Denitrification converts _____ to _____.
NO3 --> N2
51
Define rhizobacteria.
Root-associated bacteria
52
Define rhizosphere.
Thin layer of soil closely surrounding the plant's roots
53
What types of effect(s) do rhizobacteria have on the plant?
Can be detrimental, neutral, or beneficial
54
Rhizobacteria can be _____ (free-living) or _____ (living between cells of the plant itself).
1. Free-living
2. Endophytic
55
Both depend on nutrients secreted by plant cells and, in return, help to enhance plant growth by _____, _____, and _____.
1. producing chemicals that stimulate plant growth
2. producing antibiotics that protect roots
3. increasing nutrient availability
56
What element is often the limiting factor?
Nitrogen
57
In what forms can plants absorb nitrogen? What form of nitrogen can they NOT use?
1. Nitrate (NO3) and ammonium (NH4+
2. Atmospheric nitrogen (N2)
58
Nitrogen is needed for the synthesis of _____ that produce _____ and _____ that produce _____.
1. Amino acids
2.
3. Nucleic acids
4.
59
Soil nitrate is formed through a 2-step process called _____.
nitrification
60
What is the order of nitrification (i.e. what gets converted to what)?
ammonia --> nitrite --> nitrate
61
What are the steps of acquiring soil ammonium (NH4+)?
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
What enzyme facilitates nitrogen fixation?
Nitrogenase
63
What do the plant and fungi provide for each other?
- Plant provides sugars
- Fungi provide more surface area (get water and minerals)
64
What are the 2 major types of mycorrhizae?
1. Ectomycorrhizae
2. Arbuscular micorrhizae
65
Which of the following habitats has the greatest abundance of microbes?
A. Soils/sediments
B. Freshwater
C. Seawater
D. Atmosphere
E. Deep subsurface
A. Soils/sediments
B. Freshwater
C. Seawater
D. Atmosphere
**E. Deep subsurface**
66
Describe deep subsurface environments.
- Huge area: large total global biomass possibilities
- Fissures are important for water
67
What are the implications of deep subsurface environments?
Possible early Earth evolution
- Protects from bombardment
68
List the types of studies in deep drilling operations. What are the concerns for these?
- Waste disposal
- Gold mines
- Seafloor drilling projects
- Concerns: contamination (use rigorous sterile sampling processes)
69
Describe the types of microbes in deep subsurface environments.
- Diverse: autotrophic and heterotrophic pathways
- Anaerobic and aerobic respiration
