agri 51 exam Flashcards
(65 cards)
If you were to walk out into a mature forest or a farm where the soil was being well
managed, gather a handful of soil, and put it under a microscope, here’s what you
might see:
⮚(a) (a) bacteria;
⮚Up to (b) different (b) cells
⮚(c) of (c) and (c);
⮚(d)of different (d)
a. 10-50 billion ; aerobic
b. 100 million ; fungal
c. Hundreds or thousands; arthropods ; micro-arthropods
d. Thousands ; algae, protozoa, and nematodes
Roles of Soil Organisms
▪ Maintaining (a) of soil.
▪ Breakdown plant and animal tissues (b).
▪ (c) of nutrients into the (c) forms.
▪ Some are (d), but most are (d)
a. fertility, structure, drainage, and aeration
b. decomposition
c. Conversion ; plant-available
d. pests ; beneficial
Diversity of Soil Organisms
▪ (a) –the mix of species present.
▪ (b)–the capacity to use a wide variety of substrates and provide a range of ecosystem services or function.
a. Species Diversity
b. Functional Diversity
Factors Affecting Diversity
▪ The (a) and (b) of the soil are influenced primarily by the (c) (organic matter and nutrients)
▪ Other factors:
⮚Physical factors: (d)
⮚ Biotic factors: (e)
⮚ Chemical factors: (f)
a. species diversity
b. functional diversity
c. amount and quality of available food
d. moisture, temperature
e. predation and competition
f. pH, salinity, pollutants and toxic materials.
Classification of Soil Organisms
▪ Based on (a)
▪ Based on (b)
▪ Based on (c)
▪ Based on (d)
a. size
b. metabolism
c. ecological function
d. hierarchy of organisms in the soil food web
Classification based on Size
▪ Megafauna: size range (a), e.g. (a)
▪ Macrofauna: size range (b), e.g. (b)
▪ Mesofauna: size range (c), e.g. (c)
▪ Microfauna and Microflora: size range (d), e.g. (d)
a. 20 mm upward; moles, rabbits, and rodents.
b. 2 to 20 mm; woodlice, earthworms, beetles, centipedes, slugs, snails, ants, and harvestmen
c. 100 micrometres to 2 mm; tardigrades, mites and springtails
d. 1 to 100 micrometres; yeasts, bacteria
(commonly actinobacteria), fungi, protozoa, roundworms, and rotifers
Classification based on Metabolism
▪ (a)
⮚Primary producers
⮚Organisms that obtain their C mainly from (b)
⮚(c) – obtain energy from sunlight (photosynthesis).
⮚(d) - obtain energy from or (d) of various elements.
▪ (e)
⮚ Organisms incapable of making their own food from light or organic compounds.
⮚Feed on organisms or remains of other organisms to get their necessary energy to survive.
a. Autotrophs
b. CO2
c. Photoautotrophs
d. Chemoautotrophs; oxidation
e. Heterotrophs
Classification based on Ecological Function
▪ (a)-subsist on living plants.
▪ (b)-subsist on dead plant debris.
▪ (c)-consume animals.
▪ (d)-live off, but do not consume other organisms.
a. Herbivores
b. Detritivores
c. Predators
d. Parasites
Hierarchy of Organisms in the Soil Food Web
Soil Food Web
▪ First level
▪ (a)
▪ Plants, lichens, moss, photosynthetic bacteria, and algae
▪ Second level
▪ (b)
▪ Bacteria and Fungi
▪ Soil (c)–the “(c)” of the soil; Tackle the (c) to decompose materials, like green yard waste and manure
▪ (d)–the “(d)” of the soil; consume the (d) to decompose materials like straw, pine needles, bark and wood
▪ Third level
▪ Organisms that (e).
▪ These predator organisms include protozoa, beneficial nematodes and microarthropods
Note: When microbes decompose the biomass, most of the N is incorporated into microbial biomass.
As these organisms feed on the bacteria and fungi, (f) are metabolized and released back into the soil, supplying plants with a steady diet of nutrients
▪ Third level - (g); There are (g) per teaspoon of soil. (g) are (g) organisms that feed on bacteria and on each other
▪ Third level -(h); A healthy soil has from (h) per teaspoon of soil. A bacterial-feeding (h) consumes about (h) bacteria per day, and a fungal-feeding nematode consumes about (h) per day
▪ Third Level-(i); They feed on fungi and plant feeding nematodes. Chew the (i) -leaves, stems, roots into smaller pieces making it easier for fungi and bacteria to decompose
▪ Third Level-(j); Literally “(j)” which results to the development of extensive system of burrows improved aeration and drainage. After passing through the (j) gut, ingested soil is expelled as (j).
▪ Fourth level
▪ (k) prey upon the insects and the earthworms
▪ Fifth level
▪ (l) prey upon the rodents and birds
a. Primary producers
b. Consumers of organic matter and left-over nutrients
c. bacteria; cows; easy
d. Fungi; goats; tougher, hard
e. recycle plant nutrients
f. excess nitrogen and other nutrients
g. Protozoa; 100 to 100,000 protozoa; highly mobile
h. Nematodes; 5 to 500 beneficial nematodes; 100; 80 feet of hyphae length
i. Microarthropods; fresh (but dead) organic material
j. Earthworms; eat their way through the soil; globular casts
k. Rodents and birds
l. Mammal predators like foxes and racoons
Major Groups of Soil Microorganisms
Fungi, bacteria, actinomycetes, algae
Bacteria
▪ Prokaryotic, single-celled, microscopic organisms.
▪ Exhibit a greater variety of (a) than any other organism.
▪ Probably the most important in terms of their effect on soil (b).
▪ Play crucial roles in (c) of contaminated soils.
Classification of Bacteria
▪ Based on morphology (d3)
▪ Based on nutritional requirements (e4)
Grouping based on oxygen requirement
▪ (f)–requires oxygen to survive (obligate aerobes)
▪ (g)- die in the presence of oxygen (obligate anaerobes)
▪ (h)-organism prefers aerobic respiration, but is capable of switching to fermentation or anaerobic respiration if oxygen is absent.
▪ (i)-need low concentrations of oxygen.
▪ (j)–does not need oxygen but is not poisoned by oxygen.
Grouping based on pH for optimum growth
▪ (k)-grow at an optimum pH well below neutrality (7.0).
⮚ some (k) species
▪ (l)-grow best at neutral pH.
⮚ Most (l) bacteria.
▪ (m)-grow best under alkaline conditions.
⮚ (m), Natronomonaspharaonis, and Thiohalospira
alkaliphila.
Grouping based on temperature for optimum activity
▪ (n) (20 -45 °C)
▪ (n) (45 -85 °C)
▪ (n) (−20 °C to +10 °C)
▪ (n) or extreme thermophile (as high as 115 °C)
Functional groups of Bacteria in the soil
▪ (o)
⮚Breakdown of organic matter
⮚Breakdown of pesticides and other pollutants
⮚(o)
▪ (p)
⮚Form “partnerships” with plants
⮚(p) bacteria
▪ (q) (e.g., Lithotrophs or chemoautotrophs)
⮚Obtain energy from compounds of (q) instead of from carbon compounds
⮚Important in (q)
a. metabolic capabilities
b. properties
c. soil formation, organic matter decomposition, nutrient cycling, and remediation
d. colony morphology, cell morphology, Gram reaction
e. Oxygen, pH, Temperature, Others
f. Aerobic
g. Anaerobic
h. Facultative
i. Microaerophiles
j. Aerotolerant
k. Acidophiles; Thiobacillus
l. Neutrophiles; pathogenic
m. Alkaliphiles; Halorhodospirahalochloris
n. Mesophilic; Thermophilic; Psychrophilic or cryophilic; Hyperthermophilic
o. Decomposers; Release/immobilization of nutrients
p. Mutualists; Nitrogen-fixing
q. Pathogens; N, S, Fe or H; nutrient cycling
Fungi
▪ Fungi are microscopic cells that usually grow as long threads or strands called (a), which push their way between soil particles, roots, and rocks.
▪ Hyphae are only a few micrometers in diameter, but can span in length from a
few cells to many yards.
▪ (b) -they require abundant supply of oxygen and organic matter in soil.
Roles of Fungi
* Play an important role in the (c) of cellulose, hemi cellulose, starch, pectin, and lignin in the organic matter added to the soil.
* Serve as (d).
* A number of soil fungi form (e) with the roots of higher plants and helps in (e).
*(f) increases active root surface for nutrient acquisition up to (f) times
*Extension of corn root surface area through mycorrhizal fungi
Mycorrhiza
* From the Greek words (g).
* A (h) composed of a fungus and roots of a vascular plant.
* The fungus helps the plant to capture (i)
*Mycorrhizal plants are often more resistant to diseases, such as those caused by (j).
* Fungi have been found to have a protective role for plants rooted in soils with
high (k).
a. hyphae
b. Aerobic and heterotrophic
c. decomposition
d. food for bacteria
e. mycorrhizal association; mobilization of soil phosphorus and nitrogen
f. Hypha mycelium network; 700
g. “mykós” (fungus) and “riza” (root)
h. symbiotic association
i. water and nutrients (N, P, S)
j. microbial soil-borne pathogens
k. metal concentrations
Actinomycetes
* (a)
* Intermediate between (b)
* (c) and (c), like bacteria
* Produce (d) like fungi, but produce a (d) hyphae.
* On culture media, actinomycetes colonies grow slowly, show powdery consistency and stick firmly to agar surface.
* Roles:
⮚Important in the (e) in the soil, including (e).
⮚Contribute to the formation of (f).
⮚Ability to produce (g), erythromycin, tetracycline.
a. Actinobacteria
b. bacteria and fungi.
c. Unicellular ;do not have distinct cell-wall
d. conidia / sporangia; non-septate and more
slender
e. degradation of organic materials; lignin
f. stable humus
g. antibiotics–streptomycin, neomycin
Algae
● Present in most of the soils where (a) are available.
● (b)-obtain CO2 from atmosphere and energy from sunlight and synthesize their own food.
● (c)
● They can be (d)
Four main classes:
1. (e) (Blue-green algae)
2. (f) (Grass-green algae)
3. (g) (Yellow-green algae)
4. (h) (diatoms or golden-brown algae)
* Blue-green algae
*More abundant in (i) soils
* Some BGA possess specialized cells known as (i) which is the site for (i).
a. moisture and sunlight
b. Photoautotrophic
c. Aerobic
d. unicellular, filamentous or colonial
e. Cyanophyta
f. Chlorophyta
g. Xanthophyta
h. Bacillariophyta
i. tropical ; “Heterocyst”; nitrogen fixation
Importance of Soil Microorganisms
▪Microorganisms are the foundation of (a).
▪Provide key environmental services ranging from (b).
▪Play a very important role in maintaining
⮚Soil (c)
⮚(d) (e.g. Nutrient cycling)
⮚Plant (e) promotion
a. aquatic and terrestrial ecosystems
b. primary productivity to nutrient cycling and waste decomposition
c. health
d. Ecosystem functions
e. nutrition and growth
Activities of Soil Microorganisms
(3)
▪ Decomposition of organic compounds
▪ Transformation of nutrients such as Nitrogen and Sulfur
▪ Pesticide degradation
Activities of Soil Microorganisms
▪ Decomposition of organic compounds
▪ When organic tissue is added to an aerobic soil, three general reactions take place:
(3a)
▪Decomposition of organic compounds in Anaerobic Soils
▪ The products of anaerobic decomposition include a wide variety of partially
oxidized organic compounds, such as:
(3b)
▪ Anaerobic decomposition releases relatively (c)
▪ (d) and may result in the (d)
- anaerobic condition: (e)
a.
▪ Carbon compounds are enzymatically oxidized to produce: CO2, H2O, energy, and decomposer biomass
▪ The essential nutrient elements, such as: N, P, and S, are released and/or immobilized by a series of specific reactions that are relatively
unique for each element.
▪ Humus, a compound resistant to microbial action is formed.
b.
▪ Organic acids
▪ Alcohols
▪ Methane gas
c. little energy
d. Very slow; accumulation of organic matter
e. agusan marsh
Factors Affecting SOM Decomposition
(8a)
Carbon/Nitrogen ratio
*A convenient tool for predicting the (b).
*(c) is the optimum C/N ratio of organic materials for faster decomposition.
* If the C/N ratio is (d),
*The amount of N in the organic material is not enough to decompose the C.
*Soil microorganisms will take the N from the N available in the soil (d).
*As decomposition proceeds, the (e).
* When the C:N ratio falls below about 25:1 further decomposition results in (f) in the plant-available form.
*After composting, the C/N ratio of organic materials is reduced to about (g)
a. ▪ Aeration
▪ Soil temperature
▪ Soil moisture
▪ Soil pH
▪Fungi : unaffected by pH level
▪Bacteria and Actinomycetes: inhibited at pH 5.5
▪ Soil texture
▪ C/N Ratio of the organic material
b. rate of decomposition
c. 20:1
d. above 30:1; Immobilization
e. C/N ratio decreases
f. mineralization or the release of N and other nutrients
g. 14-20:1
Activities of Soil Microorganisms
*Nitrogen Fixation
*The (a)
* can only be done biologically by highly specialized groups of microorganisms in the presence of the enzyme (b) which catalyzes the reduction of N2 to NH3
*Done by certain microbes, either (c) with plants (e.g. legumes) or with animals (e.g. termites)
*This process makes N available for assimilation by plants.
- (d) cannot use atmospheric Nitrogen (N2) and cannot convert it into the useable form of
Ammonium (NH3) - However, (e) can convert atmospheric nitrogen (N2) into the useable form of ammonium (NH4)
- The plant and the bacteria develop a (f), where the two organisms live together for the benefit of both.
a. reduction of atmospheric nitrogen gas (N2) to ammonia (NH3)
b. nitrogenase
c. alone (free living) or in symbiotic relationship
d. Plants
e. Rhizobium, nitrogen fixing bacteria
f. symbiosis
Activities of Soil Microorganisms
*Mineralization/Ammonification/Decay
*Fates of NH4+: (4a)
*Rates of mineralization vary with soil (b) in the soil (aeration).
* It readily occurs in (c) soils
a. * fixed by clay minerals
* lost by soil erosion
*used by plants (NH4+)
*Volatilization (NH4+—> NH3)
b. temperature, moisture and the amount
of oxygen
c. warm (68-95°F), well-aerated and moist
Activities of Soil Microorganisms
Immobilization
* (a)
(b)
* The process in which (c) by soil organisms and therefore become (c) to crops
* Incorporation of materials with a (d) (e.g. sawdust, straw, etc.), will increase biological activity and cause a greater demand for N,
and thus result in (d)
a. Opposite of mineralization
b. Inorganic N ———>Organic N
thru Micro-organisms
c. nitrate and ammonium are taken up; unavailable
d. high carbon to nitrogen ratio; N immobilization
Activities of Soil Microorganisms
Nitrification
* Process by which microorganisms convert ammonium to nitrate to obtain (a)
Steps:
(b)
* It is important for the nitrites to be converted to nitrates because (c)
* Nitrification is most rapid when soil is (d), but is virtually halted (e).
* The nitrifying bacteria are (f) and require the presence of oxygen to produce NO2- and NO3- ions
* Nitrification can significantly (g) because of the production of H+ ions.
a. energy
b. 2NH4+ + 3O2 —-> 2NO2- + 4H+ + 2H2O
thru Nitrosomonas bacteria
2NO2- + O2 —-> 2NO3- + 4H+ + 2H2O
thru Nitrobacter bacteria
c. accumulated nitrites are toxic to plant life
d. warm (20-30 °C), moist and well-aerated
e. below 5 °C and above 50 °C
f. aerobic
g. increase soil acidity
Denitrification
* (a) through the conversion of NO3- to gaseous forms of N, such as nitric oxide, nitrous oxide and dinitrogen gas.
General sequence for denitrification:
(b)
* This occurs when the soil is (c). Denitrification is common in poorly drained soils (d)
* Bacteria responsible belong to the genera (e)
a. N is lost
b. NO3- —> NO2- —> NO ^—> N2O ^—> N2 ^
nitrate, nitrite, nitric oxide, nitrous oxide, dinitrogen gas
c. saturated, and the bacteria use nitrate as
an oxygen source
d. anaerobic
e. Pseudomonas, Clostridium, Bacillus, and Paracoccus
Activities of Soil Microorganisms
*Sulfur Transformations
* Like N, sulfur (S) also undergoes mineralization, immobilization, oxidation, and reduction through microbial activities
*Under (a), S may be (b) with a release of energy
*Under (c) as in paddy soils, sulfate may be (d)
*The end product is (e) or, in the presence of Fe, (e)
*The characteristic offensive odor of flooded soils is primarily emanating from (f)
a. aerobic environment
b. oxidized by Thiobacillus thiooxidans to SO4
c. anaerobic conditions
d. reduced by the bacteria Desulfovibrio desulfuricans
e. H2S; FeS
f. H2S
