Term
Name two types of mycorhizae and tell a little about them |
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Definition
• Endomycorrhizae
– Also called Vesicular‐Arbuscular mycorhizae (VAM)
– Arbuscules develop withinplant cells
– No root or outside structural changes
– In nearly all cultivated plants
(some trees and shrubs)
• Ectomycorrhizae
– Hyphae form compact mantle or sheath over root surface
– Hyphae penetrate between cells of root cortex
– In temperate trees and shrubs |
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Term
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Definition
• Unicellular organisms
• Some of the “simplest” and smallest forms of life
– Prokaryotic (no nuclear membrane)
– 0.5 to 5 micrometers in length
• Clay is < 2 microns, so most are larger than clay particles
– Most are chemoheterotrophs
• Numbers exceed all other soil organisms
– 1 g of soil may contain up to 108 cells
– 1 g of soil may contain up to 20,000 species |
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Term
Soil Bacteria can be classified according to C and energy sources and their oxygen requirement which are? |
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Definition
– photoautotrophs
• Energy from sunlight, C from CO2
– photoheterotrophs (rare)
• Energy from sunlight, C from organic materials
– chemoautotrophs
• Energy from oxidation of inorganic material, C from CO2
– chemoheterotrophs
• Energy and C from oxidation of organic materials
• Often just referred to as heterotrophs |
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Term
what are soil bacteria Oxygen requirement and electron acceptors? (Think of the conditions) |
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Definition
– Aerobic
• require free O2 for respiration
– Anaerobic
• must use alternative electron acceptors instead of O2
– NO3 ‐
– SO4 2‐
– Facultative
• can be aerobic or anaerobic |
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Term
What do Chemoautotrophs do? |
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Definition
• These bacteria may oxidize inorganic compounds for energy. These reactions may be important for
nutrient availability.
• Example: nitrification
(ammonium) (nitrite) (nitrate)
NH4+ → → → NO2‐ → → → NO3‐
Nitrosomonas Nitrobacter
Both NH4+ and NO3‐ are available for plant use; however NO3‐ is much more likely to be lost from
soils. |
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Term
What are (Chemo) Heterotrophs? |
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Definition
Decomposers
• Perhaps the broadest group of soil bacteria
– many different species
• Get their C and energy from:
– decomposition of organic materials
• Responsible for decomposition of organic matter and the formation of soil humus |
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Term
What is the one thing (Chemo) Heterotrophs can do? (Nitrogen cycle) |
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Definition
• Dinitrogen (N2) fixation
– Conversion of atmospheric dinitrogen (unusable by plants) into forms that are available to plants
– Symbiotic
• heterotrophic bacteria associated with plant host
– host plant provides energy and a home
– microorganism provides available N
– Non‐symbiotic
• N2 fixation by free‐living heterotrophic or autotrophic bacteria. |
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Term
Some _________________ can
fix atmospheric N (convert N2 gas to NH4) |
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Definition
Cyanobacteria ‐ Photoautotrophs |
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Term
What are actinomycetes and what do they do? |
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Definition
• Have similarities to both bacteria and fungi
– ‘filamentous bacteria’
– unicellular, no nuclear membrane
• Functions
– Break down organic matter
• Heterotrophs
• Cellulose, recalcitrant molecules
– Produce antibiotics
• Streptomycin, neomycin, actinomycin
– Produce geosmin
• the characteristic ‘earthy’ smell of soil
– Some are N‐fixers
• Important in deciduous forest soils |
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Term
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Definition
• RNA or DNA molecules covered with protein
– do not respire or carry out biosynthetic functions
– reproduce within host cells
– responsible for many plant and animal diseases |
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Term
The Soil Microbial Community is composed of what and do what? |
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Definition
Composed of bacteria, actinomycetes, fungi, (and viruses?)
– These are in competition with each other and with soil animals for available resources
The interrelationships between these organisms are complex
– Most soils contain a mixture of all of the above, but some soil conditions favor one group over another
– Interactions between organisms can be mutually beneficial, antagonistic, highly complex … |
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Term
Cryptobiotic soil crusts
are communities of ?
(desert soils) |
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Definition
cyanobacteria, algae, fungi, mosses, and lichens, common in desert soils |
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Term
Name two MOST important for
Soil Conditions and Microbial Activity |
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Definition
Soil water
– Near ‘field capacity’ is optimum
• Soil water potential is reduced under dry conditions
• Aeration decreases when soil is too wet
Aeration
– Fungi, actinomycetes, and aerobic bacteria require oxygen
– Anaerobic and facultative bacteria can utilize alternative
electron acceptors
• NO3‐, SO4‐2, Fe+3, Mn+4 |
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Term
What oter than water and aeration is important for Microbial activity? |
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Definition
pH
– For most, optimum pH is near 7.0
– Fungi tolerate acidic conditions well
Temperature
– psychrophiles (15‐20O °C)
– mesophiles (25‐37O °C)
– thermophiles (55‐65O °C)
Substrate
– Simple substrates are decomposed more rapidly than complexsubstrates, like cellulose and lignin
– Fungi decompose cellulose and lignin more effectively than bacteria |
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Term
Beneficial Effects of Soil Organisms? |
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Definition
Inorganic transformations
– Many soil redox reactions are biological
• Nitrogen fixation
– Conversion of atmospheric N2 gas to useable forms
• Organic matter decomposition
• Breakdown of toxic compounds
– Natural and man‐made (xenobiotic)
• Production of soil humus |
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Term
Tell a simplified version of the carbon cycle |
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Definition
Atmosphere to Soil:
– Via photosynthesis, plants convert C from the air into
organic forms
Soil to Atmosphere:
– Plant material returned to the soil is broken down by soil microorganisms
• some C is converted to CO2
• some C is converted to microbial biomass
• some C is converted to humus
– Humus is slowly broken down and CO2 is released to the atmosphere |
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Term
What is Soil organic matter? |
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Definition
OM is composed of living organisms, plant and animal residues in various stages of decomposition, and humus.
– Living soil organisms comprise ~ 0.2% of soil mass.
– Soil organic matter comprises 1 to 5% of soil mass in mineral soils.
• Soil organic matter is mostly C, with varying quantities of other essential elements
– Mineralization or breakdown of organic matter by heterotrophs
• cycles nutrients for plant and microbial growth
• recycles CO2 to the atmosphere |
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Term
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Definition
Humus is the dark‐colored organic residue left after decomposition of added plant or animal residues
– It is the leftover waste from microbial decomposition
• Large molecules (MW =700 to 300,000)
• Humus is variable in composition, but is usually about 58% C and about 5% N
• Humus has a three dimensional sponge‐like structure that can absorb water and solutes in the water.
– Humus is resistant to further decomposition
• Usually, only 1‐5% of soil humus is mineralized (broken down) by microorganisms each year |
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Term
Humus shares two properties with clays what are they? |
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Definition
it is highly charged and it has a large
surface area to volume ratio. |
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Term
What is hydrophobic binding? |
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Definition
• A mechanism for soil sorption of organic contaminants is hydrophobic binding.
– Hydrophobic sites are created when organic matter is present.
– Polar groups in the sponge‐like organic matter structure face the outside while non‐polar groups are in the interior.
– Nonpolar molecules are attracted to the nonpolar sites in the organic matter resulting in hydrophobic binding. |
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Term
What is the importance of soil humus? |
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Definition
Physical
– Stabilizes soil structure
– Has high water‐holding capacity
– Responsible for dark or black color of soils
Chemical
– Has high CEC
– Provides a nutrient source for microorganisms
– Provides a nutrient source (especially N) for plants
– Sorbs organic molecules |
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Term
Plant residues vs. humus
the difference? |
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Definition
Plant residues
– Un‐decomposed dead roots and other recognizable plant residues or litter
Humus
– Humus has relatively high amounts of lignin and other
complex organics
– Some less complex organics
• Organic acids
• Polysaccharides (sugar polymers)
– Colloidal
• High CEC (pH dependent charge) |
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Term
What is the mineralization of residues? |
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Definition
Plant residues are composed of a number of
compounds.
– Some of these compounds are, in order of increasing
resistance to degradation:
sugars = amino acids < proteins < starches < cellulose < fats & waxes < lignin
– The time required to degrade a residue will depend partly on its chemical composition
Larger and more chemically complex (ring structures, double bonds, etc.) molecules degrade more slowly |
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Term
Easily degraded compounds found in
plants (sugars, amino acids, starches)
are associated with young, green plant
materials
AND
The more recalcitrant compounds found
in plants (cellulose, lignin) are
associated with old, brown, and woody
materials. Name this |
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Definition
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Term
Factors Controlling Residue Decomposition |
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Definition
• Carbohydrates present in residue (lignin, etc.)
• Carbon to Nitrogen Ratio (C:N) of the residue
– Microorganisms need N to form amino acids, proteins
– They also need carbon to form build cell walls, etc.
– They need C and N in proper proportions
• Temperature
• Water
• Nutrients
• Soil pH
• Soil Texture |
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Term
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Definition
– These residues are nitrogen‐rich (C:N < 25:1)
– They contain more than enough N for microbes
– Decomposition results in a net release of available N for
plants (nitrogen mineralization) |
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Term
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Definition
– These residues are carbon‐rich (C:N > 25:1)
– They contain less N than needed by microbes
– As microbes decompose these residues they will scavenge
nitrogen from the soil solution, depleting the soil of
available nitrogen (nitrogen immobilization). |
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Term
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Definition
Net Mineralization
• Decomposition of residues with small C:N ratios results
in release of ‘extra’ nitrogen into the soil |
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Term
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Definition
Net Immobilization
• Decomposition of residues with a wide C:N ratio results
in the use and tying up in microbial tissue of the
nitrogen being released from organic matter, and also
the inorganic nitrogen (nitrate and ammonium) already
in the soil. |
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Term
Changes in microbial activity, in soluble nitrogen level, and in residual C:N ratio following the addition of either high (a) or low (b) C:N ratio organic materials.
Where the C:N ratio of added residues is above 25, microbes digesting the residues must supplement the ____________ contained in the residues with soluble
____________________ from the soil. |
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Definition
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Term
OM content decreases with ___________ |
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Definition
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Term
The quantity of organic matter found in soil depends on ___________________. |
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Definition
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Term
Soils found in _______________ ___________ with high rainfall have increased levels of organic matter |
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Definition
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Term
Grasslands, otherwise known as ___________ tend to have high OM content
– Grass residues are relatively resistant to breakdown |
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Definition
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Term
In wet soils OM breakdown is limited by lack of _____
(Histosols) |
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Definition
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Term
Name 4 effects of cultivation (tillage) on soil organic matter |
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Definition
(Why does this happen?)
1. Plowing/tillage break down aggregates, and increase
decomposition rate.
2. Crop production may increase erosion rate.
3. Removal of plant material from soils during harvest.
4. Incorporation of residues during tillage. |
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Term
SOM levels are determined by a balance (equilibrium)
between inputs and outputs what are they? |
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Definition
– Inputs
• Maximize plant growth
– Maintain adequate nutrients (especially N)
– Minimize constraints on plant growth
• Continuous supply of organic material – add plant residues, animal manures or other materials
– Outputs
• Decomposition
• Erosion |
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Term
Both conservation tillage systems leave much crop residue on or near the ___________ __________. |
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Definition
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Term
The no-till system also leaves the soil almost completely unstirred, thus further slowing ___________________. |
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Definition
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Term
What can animal manure do to soil? |
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Definition
– Animal manures contain low amounts of nutrients
compared to fertilizers
– The nutrients are released slowly as manure is mineralized
• < 50% of N is available during the first year
• Manure addition to soils disposes of ‘waste material’
– Can cause environmental hazards |
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Term
What about sewage sludge and soils? |
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Definition
• The solid residue of municipal wastewater treatment
• Most available near large cities
• Composition is similar to animal waste, but:
– Heavy metals are a concern in areas with manufacturing
• Pb, Ni, Cr
– Human pathogens are a concern
• Can’t be used on food crops
– Pharmaceuticals are an emerging concern |
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Term
Federal and State Regulations regulate allowable
rates of sewage sludge application based upon: |
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Definition
– Crop to be grown (food versus other crops)
– Crop nutrient need
• Can only apply enough to provide nutrients for plants
– Where heavy metals are a concern
• Soil pH must be > 6.5 to prevent metal movement
• Soil with high CEC hold metals better |
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Term
The liquid resulting from wastewater treatment is? |
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Definition
– Valuable for irrigation, and contains dissolved
nutrients
– Widely used in the Southwest for
irrigating golf courses and parks
• including UA campus – look for the
purple plumbing
– Concerns are similar to those for
using sewage sludge |
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Term
What is composting?
(scientific not just decomposing veggies!) |
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Definition
• The aerobic breakdown of organic materials which
results in a mass of partly decomposed organic matter.
– Carbon is lost, so C:N ratio decreases
• Less likely to cause nitrogen immobilization
– Weed seed, pathogens, reduced
– Compost, like animal manure, is not nutrient‐rich
• Contains much less nutrients than fertilizers |
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Term
What are the stages of composting? |
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Definition
1. initial mesophilic stage
2. thermophilic stage
3. final mesophilic or curing stage |
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Term
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Definition
• Breaking down toxic compounds with soil microorganisms
– Simple hydrocarbons (fuel oil, gasoline, lubricants) are
similar to organic residues and are decomposed by soil
bacteria
– Complex hydrocarbons (e.g. PAHs) are more difficult to break down
– Halogenated xenobiotics (PCBs,
PCPs, TCE, etc.) are very resistant
but can be broken down
• anaerobic bacteria
• soil fungi |
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