Exam #3 Flashcards
what are the three domains of life?
-eukaryota
-bacteria
-archaea
generally, what type of organisms are eukaryotes?
fungi, protists, plants, and animals (membrane bound organelles with nucleus)
what type of organisms are prokaryotes?
archaea and bacteria (don’t have membrane-bound organelles)
describe the kingdom protista
very diverse eukaryotes that are a part of an “other” category that aren’t plants, animals or fungi; some can move and photosynthesize, some form colonies such as slime molds and kelp.
describe the soil trophic levels
primary producers –> primary consumers (herbivores) –> secondary consumers –> tertiary consumers
decomposers: consume all dead organic matter and release plant nutrients (all trophic levels)
primary decomposers:
>detritivores: eat dead or digested plant debris
>saphrophytes: eat dead or digested plant and animal debris (responsible for most decomposition)
what are the different size classes of soil organisms?
- macro-organisms (>2 mm)
- meso-organisms (0.1-2mm)
- micro-organisms (<0.1mm)
what organisms are considered macro-organisms?
-plant roots
-burrowing animals
-earthworms
-ants and termites
__________ _______ are macro-organisms which are ____-____ of plant mass. they are ___-______ um in diameter
plant roots
30-50%
10-400
how do plant roots enrich SOM?
roots enrich SOM with:
exudates: dissolved organic compounds exuded by roots
ex: acids, sugars, mucigel, shedded cells, dead roots
-root respiration (1/3 to 1/2 of soil CO2)
-create biopores
what is the rhizosphere? what does the rhizosphere has more of compared to non-rhizosphere soil?
zone most affected by roots (2-3cm of roots)
the soil in the rhizosphere has
-more SOM (more sugars)
-more chelates –> increased complexation
-lower nutrients (more acids)
-lower O2, more CO2 (due to more respiration)
-lower aeration
(compared to non-rhizosphere soils)
describe burrowing animals that contribute to macro-organisms and how they impact soils
diverse species and trophic levels: mammals, reptiles, insects, and amphibians (multiple ecological roles: detritivores, predators, and herbivores)
soil impacts: translocate and mix soil, create networks of biopores, and aerate soils
ants and termites have multiple ecological roles (herbivores, predators and detritivores), how do their nests impact soils?
-improved soil aeration
-increased infiltration
-modify soil pH
-local enrichment of nutrients
(habitat for ants: temperate, for termites: hot, dry)
what habitat are earthworms (Annelida) found in? what are their functions?
cool, moist aerated soil with neutral pH; most abundant animal microorganism in moist humid regions.
functions: mix soil particles and nutrients, improve soil structure (increase aggregation)
what are different types of meso-organisms?
rotifers
springtails and mites
tardigrades (“water bears”)
nematodes (unsegmented worms found in almost all soils)
protozoa
describe protozoa and where you might find them
mobile, unicellular eukaryotes of the kingdom protista (some photosynthesize). they are predators who eat bacteria, 4-250 um in size. habitat: prefer moist, aerated surface soils
what 4 things do all organisms need to survive?
-electron acceptor (oxidizing agent)
-carbon source
-water
-mineral nutrients
where do autotrophs get their carbon/energy from?
C from inorganic compounds (CO2 or CO3 2-)
where do heterotrophs get their carbon/energy from?
C from organic compounds (with C-C and C-H bonds)
where do chemotrophs get their energy from?
energy (e-) from chemicals
where do phototrophs get their energy from?
energy (e-) from light
what are chemoheterotrophs?
energy source from biochemical oxidation and carbon source from organic materials (all fungi, all animals, most bacteria)
what are chemoautotrophs?
energy source from biochemical oxidation and carbon source from CO2 (deep ocean microbes, N + S oxidizers)
what are photoheterotrophs?
energy source from sunlight and carbon source from organic materials (some bacteria, algae and protists)
what are photoautotrophs?
energy source from sunlight and carbon source from inorganic CO2 (algae, cyanobacteria, and higher plants)
what 8 environmental conditions affect soil microbial growth and activity?
- organic substrates
- nutrient substrates
- oxygen/redox status
- temperature and sunlight
- moisture
- pH
- salinity
- toxins
what is the Baas-Becking Hypothesis?
everything is everywhere but the environment selects
most soil microbes prefer when soil water content is near ________ __________
field capacity (too dry = microbes can’t get water or solutes)
how does soil aeration affect soil microbes?
good aeration –> aerobic microbes dominate = faster growth and decomposition
too much water (saturated) –> low aeration (low O2)
–> anaerobic respiration = slower growth and decomposition
(alternative electron acceptors = NO3-, SO4 2-, Fe3+, and Mn4+)
what is the ideal pH and temperature range for soil microbes?
optimal pH is near 7 (fungi tolerate acidic conditions well)
temperature:
-thermophiles (55-65 degrees C)
-mesophiles (25-37 degrees C)
-psychrophiles (15-20 degrees C)
simple substrates are decomposed _____ _______ than complex substrates, like cellulose and lignin.
_________ decompose cellulose and lignin more effectively than __________
more rapidly
fungi
bacteria
what are algae, what effect do algae have on soils, and what habitat are they found in?
photoautotrophs (protista and plantae, 2-20 um)
soils effects: add OM and microbiotic crusts
habitat: need a fairly moist environment and mostly at soil surface (for light)
what are slime molds? where are they found in the soil?
protists (eukaryotes): amoeba-like cells that spend most of the time as single cells; they form colonies.
-colonies form networks and possibly also think
ecology: feed on bacteria and can congregate together into 0.1mm mounds
habitat: live in O and upper A horizons
what are fungi? what impact does fungi have on soils?
eukaryotes; most are filamentous (hyphae = root-like filaments) (mycelia = woven hyphae) can be uni- or multi- cellular. (yeasts, molds, mushrooms)
-chemoheterotrophs (mostly saprophytes)
soil impacts:
-slow steady decomposers
-soil aggregate binding with hyphae
what are mycorrhizae?
fungi that form a symbiosis with plants (found in 90% of plant species’ roots)
-plant roots provide sugars and a home for fungi
-mycorrhizae provides plants with nutrients, drought tolerance, and pathogen protection
there is also ___________ fungi that eat __________
predatory
nematodes (releases enzymes to break down the nematodes)
describe bacteria and archaea
-no cell nucleus, asexual reproduction
-very common in soils, esp. bacteria
-smaller than protists and fungi (~0.5-5um)
-the most numerous and diverse organisms as we know it
what are actinomycetes? where are they found?
filamentous bacteria (0.5-5um in diameter) that are unicellular heterotrophs
-habitat: most soils, especially arid (alkaline, dry soils)
what functions do actinomycetes do?
- OM decomposition
- produce antibiotics
- some are N-fixers
- produce geosmin (a molecule that “smells like rain”
what are cyanobacteria (blue green algae)? what habitat are they found in?
prokaryotes (most common photoautotrophs)
-no chloroplasts (first photosynthesizers to evolve)
habitat: primarily aquatic, soil surface (0-0.5cm), biological soil crusts
prokaryotes ______ to soil ________
adsorb to soil particles (bacteria has a net negative charge and is adsorbed through a cation bridge)
what are soil viruses?
contain RNA or DNA with protein exterior
smaller than prokaryotes (most are <0.1um)
list main soil organisms from largest to smallest
-earthworms, ants and termites (largest)
-nematodes, mites and springtails
-protists
-fungi
-bacteria and archaea
-viruses (smallest)
what are lichens?
a mutualistic symbiosis between algae and fungus and they form the basis of the food chain in some areas.
what are cryptobiotic soil crusts?
mutualistic communities of cyanobacteria, mosses and lichens, common in desert soils and they protect soil from erosion, and they provide a significant amount of N to the ecosystem
how do microbes help plants?
-SOM formation
-nutrient cycling
-toxin breakdown
-disease suppression
how do microbes harm plants?
-herbivorous nematodes
-soil-bourne plant diseases
-deleterious rhizobacteria
what are 3 mutualistic plant-microbe relationships?
- rhizobia
- rhizobacteria
- mycorrhizae
what are rhizobia?
symbiotic N-fixing bacteria in legume root nodules (convert unavailable N2 from atmosphere to available NH4+)
what are rhizobacteria?
all bacteria adapted to living in the rhizosphere (mutualistic, parasitic or commensalism)
what are mycorrhizae?
symbiotic fungi found in/on most plant roots (increase P uptake and provide fungi with sugars)
____________ _____________ soils have very healthy microbial populations that help suppress plant pathogens
disease suppressive
microbes can let plants know that there are ___________ and allows the plant to release ________ ___________ against the pathogen (induced systematic resistance)
pathogens
chemical defenses
what does net carbon pool size equal?
change in C = C input - C output
what is the difference between organic C and inorganic C?
organic C has C-C and C-H bonds (in SOM: microbial biomass, humus, and detritus)
inorganic C does not have C-C and C-H bonds (soil carbonates: primarily CaCO3 and MgCO3)
what is SOM?
material derived from living things in various stages of decomposition (+ microbes)
what does SOM equal?
SOM = microbial biomass (living microbial tissue) + detritus (nonliving tissue from plants, animals, fungi, prokaryotes) + humus (decomposed, amorphous, and compost-like)
what soil order has the lowest organic matter?
oxisol; in a warm, moist environment like a tropical rainforest, microbes decompose fresh detritus very fast, and the outputs are just as high as the inputs
what is the difference between humus and detritus?
detritus: un-decomposed dead roots and other recognizable plant residues (or manure)
humus: mostly large, complex organic molecules with some less complex organics, mostly colloidal with high CEC, amorphous, brown and mushy
what is decomposition?
physical breakdown and chemical transformation of large organic molecules into simpler compounds, and synthesis of new compounds from these simple compounds
what are 4 chemical decomposition processes?
- oxidation: C –> CO2, CH4 + 2O2 –> CO2 + 2H20
- release: insoluble (solid, not bioavailable) –> soluble (solution, bioavailable)
- synthesis: of new “humic” compounds (tissues, secondary metabolites) by microbes (humification)
- protection: protecting new or partially broken-down compounds through physical or chemical means
what type of molecules decomposes slower and faster?
simpler and smaller molecules decompose faster:
sugars, starches and simple proteins (fastest)
crude proteins
hemicellulose
cellulose
fats and waxes
lignin’s and phenolic compounds (slowest)
what is mineralization?
conversion of a nonmetal from organic to inorganic form (organic nutrient = nutrient bonded to C)
-breaks bond between the nutrient (P, N, S) + C, causing the nutrients to become more plant available
the ______ nitrogen there is in a soil, the faster the decomposition rate
more
_________ and ________ have a C/N ratio of 5-10:1
microbes and manure
-manure has C/N ratio ~6:1 because it has so many microbes
-bacteria/archaea > actinomycetes/nematodes > fungi
_______ and ___________ have a C/N ratio of 8-15:1
SOM and compost
-SOM C/N is lower for subsoils than surface layers
(O horizons have higher C/N ratios of ~40:1)
________ __________ have a C/N ratio of 13-600:1
plant residues
-legumes have ________ –> more N –> ________ C/N ratios
-younger and greener plants –> ______ proteins –> _______ C/N ratios
-older, woodier –> _______ lignin –> ________ C/N ratios
rhizobia, lower
more, lower
more, higher (slower decomposition)
_________ C/N ratio = faster decomposition
_________ C/N ratio = slower decomposition
lower
higher
what happens when C/N ratio is more than 25:1?
-N becomes limiting factor to microbial growth
-net N immobilization: inorganic N –> organic N (organic N is N bonded to C)
what happens when the C/N ratio is less than 15:1?
-N not limiting at first –> very rapid decomposition
-net N mineralization: organic N –> inorganic N (ammonium or nitrate which is readily available for plant uptake) (mineral N = inorganic N)
what is priming?
stimulation of SOM decomposition following addition of fresh C substrates
______________ turns out to be more important than chemical composition on the effect of SOM
protection
what is protection?
microbes that are prevented from accessing and hence decomposing SOM
what is the difference between chemical and physical protection?
chemical protection occurs when SOM is actually stuck between clay particles and is chemically adsorbed to clay versus physical protection is when SOM is physically surrounded by silt or clay particles and the microbe can’t reach it
what are Terra Preta soils?
“Amazonian dark earths”, soil rich in SOM and char
what is black carbon?
carbon in char, charcoal, soot; degrades very slowly
-pyrolysis (“charring”)
-pyrolysis + oxidation –> combustion (produces oils, gasses, and char)
black carbon, including char is made up of what?
pyrolyzed (incompletely combusted) organic materials, usually plants
what soil order is heavy in char?
mollisols
what biochar?
char for adding to soil (helps acidic soils; its structure enables a very slow decomposition rate)
what are the three soil organic matter carbon pools?
- active: fast cycling, labile (largest pool)
- slow: semi-recalcitrant (medium pool)
- passive: very slow cycling, very recalcitrant (smallest pool)
in general, SOM ___________ exponentially with increased depth (except for spodosols)
decreases
with increased drainage, there is _______ aeration, _______________ decomposition and _______SOM
increased
increased
less
with decreased drainage, there is __________ aeration, __________ decomposition and ______ SOM
decreased
decreased
more
drainage of thawed permafrost + wetlands causes what
release of CH4 and CO2 (GHG’s)
anaerobic decomposition of SOM is ______ _________ than aerobic decomposition
much slower (less O2 –> can’t oxidize CO2 –> less energy)
with an increase in soil temperature, there is ______ plant growth, _________ aerobic decomposition (or anaerobic), which causes ________ SOM
increased
increased
less
with more clay, there is __________ aggregation, _______ protection of SOM, __________ SOM degradation, and ______ SOM
increased
better
slower
more
what are carbon inputs and outputs for SOM?
inputs: plant litter/residues, animal waste, imported bio-products, root residues, rhizodecomposition
outputs: CO2 oxidation, erosion, removal, organic C, leeching and dissolved
with more tillage, there is ________ erosion, ____________ SOM outputs, causing _________ SOM
more
increased
less
with more tillage, there is ____________ aggregation, ________ protection and _________ O2, _________ SOM outputs, resulting in ______ SOM
decreased
decreased
more
increased
less
with crop harvesting, there is _______ detritus additions, causing a ________ in SOM inputs, and results in _______ SOM
decreased
decease
less
with crop rows there is ______ bare soil, _________ erosion, __________ SOM outputs which results in ______ SOM
more
increased
increased
less
after drying to eliminate water in plant litter, which 2 elements account for ~80% of the dry weight?
carbon and oxygen
under natural vegetation, about 60-90% of SOM is in the __________ fraction
passive, very recalcitrant and/or well protected
what are the top 4 techniques for managing SOM?
-reduced tillage
-organic amendments
-erosion control
-cover crop and perennials
conservation tillage leaves _____ of plant residues on the surface
~30%
with less tillage, there is _______ erosion, __________ aerobic respiration and _____ SOM outputs
less
reduced
less
increased soil cover and decreased slope –> ________ water flow –> _________ erosion
slower
less
what are cover crops? what are perennials?
cover crops: growing additional crops between growing seasons.
perennials: plants that grow year round
with less erosion, there is _______ OM outputs. what are examples of how to control erosion?
less
ex: contouring, terracing, and grass strips
when plants deposit detritus year-round, there is _______ OM inputs
more
what are 6 things you can add to soils as an organic input?
-sewage sludge
-biowastes
-compost
-biochars
-manure
-grey water
what is composting?
intentional aerobic breakdown of organic materials outside the soil to form decomposed OM.
-mixed to promote aeration
-reduced weed seeds and pathogens
-optimal C:N ratio (~10)
-has dilute, organic nutrients
adequate, not excessive ___________ is best for managing SOM
nitrogen
how does mulch used to manage SOM?
mulch covers the soil and reduces erosion. (only plant-based mulches increase OM inputs)
what is soil fertility?
ability of a soil to supply nutrients and provide favorable conditions for plant growth
what are the macronutrients found in soils?
from air and water: C, H + O
from soil: N, P, S, Ca, Mg, K, Si
(greater than 0.1% of plant mass)
what are the micronutrients found in soils?
from soil: Cu, Fe, Mn, Ni, Zn, Mo, B, Cl, Na, Co
(less than 0.1% of plant mass)
both ____________ and ___________ consist of 1-6% of dry plant mass fraction (plants contain ~90% water)
nitrogen (N) and potassium (K)
explain why nitrogen is so important for plant growth
- nitrogen is the soil macronutrient that plants use the most and is commonly the most limiting nutrient for plant growth
- nitrogen is essential for amino acid, protein, and enzyme synthesis
N fertilizers are needed for ____-___% of U.S. food production
30-50%
nitrogen is readily _______ from agricultural soils: 30% goes into the _________ and 30% goes into ___________
lost
atmosphere
groundwater
(nitrogen losses can be reduced but not 100% prevented)
how does N pollution from agriculture and industry affect the environment?
-water quality
-aquatic biodiversity
-air quality
-human health
-climate change
what is a real-world example of how nitrogen affects water quality?
the gulf of Mexico’s dead zone (April 2017)
what does it mean to be organic nitrogen? what are the most common forms of organic nitrogen?
N bound to a C in 1. humus (~5% N) or 2. organisms and detritus (1-20% N) (not plant available)
most common forms:
-urea ((NH4)2CO) (sometimes plant available)
-amines
-amides
more than ____% of topsoil N is organic
95%
what does it mean to be inorganic nitrogen? what are the most common forms of inorganic nitrogen?
N not bound to C
in soil solution (ions with charge) (plant available):
-ammonium (NH4+)
-nitrite (NO2-)
-nitrate (NO3-)
in soil air: (not plant available)
-nitrogen gas (N2)
-nitrous oxide (N20) (GHG)
-nitric oxide (NO) (acid rain contributor)
-nitrogen dioxide (NO2)
-ammonia gas (NH3)
the smallest pool of nitrogen is more _______ __________ versus the largest pool is _______ ____________
plant available
plant unavailable
which N pools are a direct source of N for plants?
- the soil solution
- adsorbed to colloid exchange sites
describe the size of nitrogen pools from largest to smallest
largest: atmosphere –> soil organic nitrogen (SON: microbes, detritus, humus) –> adsorbed to colloids –> dissolved inorganic nitrogen (smallest)
generally, what are the 3 main soil N cycling fluxes?
- additions (inputs): N2 fixation, OM decomposition, rainfall, fertilization
- transformations/translocations: immobilization, mineralization, nitrification, desorption, adsorption, downward movement of soluble N in soil profile
- losses (outputs): denitrification, NO3- leaching, and NH3 volatilization
what is nitrogen fixation?
conversion of N2 –> NH3, NH4+, and/or NO3-
lots of energy is required to break the triple N bond in N2, where does this energy come from?
- biotic: microbes
- abiotic: lightning or industrial fertilizer synthesis (Haber-Bosch process)
___________ living in ________ root nodules convert N2 into NH3 and are responsible for the most biotic N fixation
rhizobia
legume
(legumes = pea family (Fabaceae plants –> beans, chickpeas, lentils, peanuts, clover, and mesquite))
some ___________ also fix N for shrubs and trees (ex: Frankia in alder trees)
actinomycetes (filamentous bacteria)
______ _________ N fixing bacteria also fix some N
free living
(non-symbiotic is much less abundant)
(cyanobacteria and some heterotrophs)
symbiotic land plant fixation is ______ _________ than non-symbiotic fixation
more abundant
(rhizobium + legumes –> cyanobacteria –> free living)
what 5 processes are considered to be an addition in the nitrogen cycle?
- haber-bosch process (N2 fixation)
- lightning (N2 fixation)
- rhizobia and frankia (N2 fixation)
- acid rain (N deposition)
- fertilization//OM application
how does lightning fix nitrogen?
lots of naturally supplied heat and energy breaks the N-N triple bond in N2 and allows N to react with O in atmosphere to form NO and NO2. (abiotic and natural N fixation)
how does the haber-bosch process fix nitrogen?
N2 gas is reacted with H2 gas under high heat conditions to break the N-N triple bond and form NH3 (abiotic and anthropogenic N fixation)
(50% of all global N2 fixation)
how does acid rain contribute to N deposition?
combustion of fossil fuels leads to SOx and NOx emissions. the SOx and NOx then react with H20 in the atmosphere to produce sulfuric and nitric acids. these acids then dissociate and produce loose H+ ions which lowers the pH of water droplets in the air which then coalesce and fall to the ground and into soils
what are organic nitrogen additions?
- organic fertilizers (synthetic urea)
- composts, mulches, plant residues
- manure (human applied, deposited by animals)
- wastes (grey water, urine, biosolids (from sewage treatment plants))
what 5 general processes are considered transformations and translocations?
- N uptake by plants
- mineralization
- immobilization
- nitrification (ammonium oxidation)
- adsorption and desorption
plants take up mostly ________ and _________ and some urea. plants use ___________ N to synthesize ___________ N (proteins, enzymes, etc)
NO3- and NH4+ (both plant available)
inorganic
organic
mineralization and immobilization occur ____________
simultaneously
N ___________ makes N available to plants and is favored by OM with a C:N ratio of _________
mineralization (organic N –> inorganic N)
less than 15:1
