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SCSC 301 EXAM 2 TAMU SMITH QUESTIONS
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SCSC 301 EXAM 2 TAMU SMITH QUESTIONS
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SCSC 301 EXAM 2 TAMU SMITH QUESTIONSAn organism that can use CO2or CO3- (i.e., inorganic C) as a C source, and obtain
energy from the sun (photo) - or from the oxidation of inorganic elements or compounds
such as iron, sulfur, hydrogen, ammonium, and nitrites (chemo)? - Answers-Autotroph
such as plants, algae, cyanobacteria, etc.
An organism that can only get carbon and energy from organic compounds? - Answers-
Heterotroph such as bacteria, fungi, protozoa, etc.
An organism that grows only in the presence of molecular oxygen? - Answers-aerobe
such as nitrifying bacteria
Plant roots - Answers-release C into soil via exudates, aid in aggregate formation, use
O2 for respiration (produce CO2)
Earthworms - Answers-eat detritus (waste), organic matter and microorganisms, form
burrows, "nature's tiller" create casts- aggregation
Termites - Answers-complex social colonies, mound builders, symbiotic gut microbes
degrade cellulose, fungi farmers
Nematodes - Answers--microbial predator- controls populations and releases plant-
available N
-moist, well-aggregated soils
-moved by pushing or "swimming"
Tardigrades - Answers-abundant in mosses and
Lichens, pioneer species, eats algae, bacteria, plant cells and mesofauna, called water
bears, moss piglets
Protozoa - Answers-mobile, single-celled bacterial predators; amoeba, ciliate,
flagellates; moist, well-aerated surface soils
Algae - Answers-photosynthetic, autotrophs, primary producers; wet surface soils; can
form symbiotic relationship with fungi to form lichen
Fungi - Answers-eukarytoes, heterotrophic, diverse morphology, moist environments;
can be single-celled yeasts, filamentous molds or mushrooms with macroscopic fruiting
bodies
Bacteria - Answers-prokaryotes, most abundant and diverse in soils; important for many
soil functions(bioremedation, decomposition, nutrient cycling)
, Actinomycetes - Answers-filamentous bacteria (branching morphology), aerobic
hetertrophs, non-acidic, moist, high C environments; produces antibiotics compounds,
some fix N especially in forests (frankia sp.)
Rhizobia - Answers--N-fixing bacteria
-Forms root nodules in leguminous plants
-important in grasslands and agricultural systems
Mycorrhizal fungi - Answers-symbiotic with plants, gets C from plant roots, provides
water and nutrients especially Phosphorous to plants
-provide protection to plants
Saprotrophic fungi - Answers-gets C from ecosystem, degrades organic matter,
important for lignin degradation and SOM decomposition
Prime conditions for high microbial activity - Answers--Carbon availability
-quality C:N
-oxygen availability (greatest zone of activity is top 5 cm of soil bc good balance of O
and H20
-Good temperature is 20C-40C
-High calcium and neutral ph soils
-bacterial diversity increases with soil ph (acidic to alkaline soils)
Soil microbiome includes - Answers-prokaryotes (bacteria), eukaryotes, and archaea
Stable Organic Matter (humus) slow pool - Answers--Stable C, protected from more
degradation! Could be from mineral sorption, isolation in micro-aggregates, an
unfavorable environment. Overall, conditions that limit microbial access to and
degradation of C
-POM, biomolecules, degradation, complex molecules like lignin and phenols
-Biochar (VERY stable, charcoal)
-Colloidal characteristics: High surface area, High Cation exchange capacity (holds onto
cations or nutrients), High water holding capacity, negative charges, dark color
Labile organic matter (Fast pool) - Answers--living biomass
-free (detritus, POM, biomolecules, degradation products)
-O horizon
SOM - Answers--Decomposing Organic matter-Most active about 33-55%
-Fresh residues is about 10%
-Living organisms is about 5%
-Stable organic matter (humus) is about 33-50%
Sources of Carbon in soils - Answers-Plant tissue, animals, earthworms, termites, ants
and dung beetles or soil microorganisms
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