final Flashcards
what observations did we make on the spodosol soil monoliths?
there are horizons in the soil - sandier at the top, the bottom was more dirt like
less decomposed fresh leaves at the top
found bugs and plants and roots and leaves!
what four earth domains come together in soil? in which ways are each domain present and incorporated in soil
lithosphere, hydrosphere, atmosphere, biosphere
lithosphere is the parent material, hydrosphere is the water within the soil that is home to organisms, atmosphere is the carbon within the soil, and biosphere is the organisms!
what are the major components of soil and what are their approximate proportions
mineral matter (45%), air (25%), water (20%),
!!!!!!!!!!!!what are the three soil mineral particle sizes? how do their sizes influence their soil surface area, pore sizes, and water holding capacity? apart from their sizes, what is different about them (surface charge, primary vs secondary materials) and what are the consequences of those differences?
sand, silt, clay
sand is the largest, silt is medium, clay is smallest
texture impacts surface area which impacts the ability to hold materials (clay has lots of surface area
what is the physical and ecological significance of soil pore space? what is ecologically significant about macropores?
pores contain air and water which are essential for the life of soil, without pore space organisms wouldnt live in soil
pore space/water allows microbes to move
oxygen in pore space to contribute to function of aerobic organisms
does healthy soil have a diversity or uniformity of pore sizes? why does that diversity or uniformity make it healthy?
diversity - this gives a home for many different sized organisms within the soil which promotes diversity in organisms
what are the causes and consequences of soil compaction
soil compaction leads to smaller pore space which makes it harder for air and water to live in soil, this makes it harder for organisms to live in the soil
this is caused by tractors, cars, and people walking
reduces infiltration of rainwater (increases erosion)
figure 4.8
what taxa of soil organisms are responsible for ~95% of terrestrial decomposition? what ecological advantages or disadvantages does each taxa have (under what circumstances would you expect one or the other to be favored or not favored)
fungi and bacteria
fungi - decomposes dead plant material and transport nutrients over long distances, can live in less nutrient filled soil, are unable to survive in anaerobic soil and aquatic sediments
bacteria and archaea - if conditions are good they rapidly absorb substrates and grow (multiply and decompose) quickly, can exhaust substrates in immediate environment and they become inactive, can live in so many different environments (and go dormant) bacteria are stuck and cannot transport materials
why do bacteria produce biofilms, and what are the consequences for soil structure
biofilm protects bacteria from grazing protozoa and reduces bacterial water stress by holding water like a sponge
increases efficiency of bacterial exoenzymes by preventing them from being swept away by moving water
dormancy in bacteria: why and to what extent
metabolically dead but still alive
expending no energy - can still respond to queues from the world and then revive
results from a lack of nutrients in the soil that support active life
can survive a lot more in dormant state
reactivated in the presence of labile substrates
what are the main ecological roles of soil microfauna, mesofauna, and macrofauna? what are their effects on decomposition
microfauna - protozoa and nematodes alter the population of bacteria and fungi
mesofauna - shred things ! increasing surface area which helps bacteria and fungi to break things down (decomposition)
macrofauna - ecosystem engineers, moving things around and increasing decomposition by making things more or less accessible for bacteria and fungi
in which of the four earth domains do soil bacteria and microfauna exist
mainly in water
why is the rhizosphere a special place, ecologically
plans exude things into the soil, hot spots of biological activity
lots of bacteria and protozoa
what are the major classes of organic material present in soils? which are primarily labile carbon and which are primarily soil humus and what are the important distinctions between the two categories
labile carbon - rapid turnover, living organic biomass, identifiable dead tissue, free bits of partially degraded tissue, free or dissolved biomolecules, fungi and bacteria exude enzymes which break down plant litter which creates dissolved organic carbon which is absorbed by the fungi and bacteria again
humus - slow turnover, protected bits of degraded cell walls and tissue, protected biomolecules, supermolecules, black aromatic products of fire
depends on the degree of which component compounds are protected from decay by soil environment (mineral particles or aggregates) - char (dramatically different carbon makeup), inaccessible inside micro aggregate and the carbon cannot be accessed, protected by sorption - minerals can be stuck inside
by what mechanisms is soil carbon protected from further decomposition and thus able to contribute to carbon sequestration
flocculation, volume changes in clay-ey materials, burrowing and molding of animals, enmeshment of particles by sticky networks of roots, production of glues by microorganisms
what is the hierarchy of aggregation
small aggregates build up to larger aggregates (theyre all basically the same thing because they build upon each other), small aggregates are more stable than large ones
at what scale are physical-chemical processes most important for aggregation? what is flocculation? how does shrinking and swelling contribute to aggregation
flocculation creates clay clumps, shrinking creates cracks that compress into aggregates (result of temperature and moisture changes) - most prominent in soils with high swelling rates
at what scale are biological processes most important for aggregation? what are those biological processes? why does each one exist (from the organisms’ perspective) and how does it contribute to aggregation
biological processes create more aggregation that sticks to the clay (sticks smaller stuff together)
larger things get stuck with enmeshment (the roots are growing and creating stick material to make their job easier) and burrowing and molding (earthworms moving through the soil, creating sticky substances that stick particles together)
influence of organic matter - gives soil energy for biological processes
why is soil organic matter so important to soil aggregation
organisms create sticky substances
burrowing and molding
enmeshment by sticky roots and hyphae
polysaccharides produced by bacteria
soil organisms require carbon, and without soil organisms soil aggregation may be weaker
it fuels biological processes
in what ways does tillage directly influence a farm’s soil aggregation and soil organic matter (and thus also indirectly influence soil aggregation)
can promote and destroy aggregation
in the right conditions, tilling can create natural aggregates increases rate at which soil organic matter oxidizes, can destroy aggregates
without organic matter, there is no food for microorganisms which are important in creating soil aggregation
over time, tilling weakens aggregates
is soil texture (percent of sand, silt, and clay) the same thing as macroaggregates, microaggregates, and sub-microaggregates
no!
soil texture - sand, silt, and clay and the makeup that creates soil
aggregation - when bits of soil (may contain sand silt and clay) get stuck together
why do water molecules adhere to charged surfaces and cohere to each other
because the hydrogen and oxygen atoms are attached in a “v” arrangement, they stick together as a result of the molecules’ charges
cohesion - water molecules are attracted to each other because of polarity
adhesion - soil particles have water particles in them that cohere to other water particles
what is the soil plant atmosphere continuum? how does it work? what are the consequences of xylem cavitation (when the continuous column of water breaks inside a plants xylem)
relative to the atmosphere, the soil is highly saturated with water
because of cohesion and adhesion, plants have columns of water that are unbroken that brings water up through the plant
droughts or injury can cause water column to be broken which makes it challenging/impossible for plants to take up water
what is the difference between evaporation and transpiration, and what is evapotranspiraton
evaporation - water exuding from soil
transpiration - water exuding from plant (leaves)
evapotranspiration - water transferring from land to atmosphere by evaporation from the soil and by transpiration from plants
does more water leave the land due to evapotranspiration or via rivers
evapotranspiration
what is the relationship between evapotranspiration, gravity, and matric forces on soil water? how are these related to “field capacity” and the “permanent wilting point”
field capacity - when soil has taken as much water without being able to freely drain
permanent wilting point - when normal plants will be unable to take up water from soil because it is held too tight to particles
matric forces - adhesion and cohesion working together
gravity is stronger than matric forces when the water is farther away from soil particles
evapotranspiration is stronger than gravity (evapotranspiration can pull water at field capacity)
!!!why is the concentration of carbon dioxide higher in soils than in the open atmosphere
oxygen is being consumed in the soil and turned into CO2
there are so many organisms in the soil that interact with oxygen and create CO2 that the outputs are incredibly high
how is oxygen diffusion into soils affected by soil water
when there is more water O2 contents will be lower
oxygen diffuses slowly through water which makes it harder for oxygen to enter soils
in what ways is oxygen availability heterogenous in soils
deeper into the soil has less oxygen
water content impacts
anaerobic vs aerobic aggregates impact oxygen availability
how does temperature affect soil processes
warmer temperatures makes it easier for decomposition
respiration increases with temperature
microbial activity increases with temperature
how do each of the components of CLORPT influence soil development
climate - breaks up rocks and modifies physical characteristics, rates of decomposition
organisms - organic matter, bioturbation
relief - landscape positions
parent materials - creates soil horizons
time - .01-.1 mm of new material per year
what are the four USDA soil orders we have been using in all of our class analyses and what are their general characteristics and the contexts in which they tend to form
HOW DO THEY DEVELOP
histosol - super wet, lots of organic materials, high carbon storage
mollisol - moist grassland, accumulation of organic matter
alfisol - moist, mildly acidic, clayey, good fertility
spodosol - acidic, accumulation of humus, not agriculturally productive
what are the four processes that - together with gravity and the inescapable up/down nature of soil - lead to soil horizons
transformation - decomposition (modifications of material)
translocation - movement of something (nature remains the same) (water can move without changing its nature)
additions - rain, poop, leaves
losses - gaseous loss, farmer removes food from soil, leaching into groundwater
what are the general soil horizons O, A, B, C, and R, and what are their basic characteristics
o - organic, topsoil, plant leaves and animal residue
a - 10 inch deep, root filled, mineral and humus
b - 30 inch deep, subsoil
c - 48in deep, unconsolidated material, barely soil
r - rocks!
relative to the soil horizons and the “drip line”, how do real root systems tend to grow
drip line - where the edge of the plants crown is (where the vegetation stops)
the root system does not mirror the drip line, the root system extends past the drip line
in what ways are higher-order roots different from lower-order roots
first order - finest roots on the absolute end of the system, acts like leaves, interacts with the environment a ton
going up the order moves from things like leaves to more branches and trunks (moving things within the plants and providing structure)
high order roots - structural and functional (moving things around) purposes
in what ways do roots add carbon to the soil
dead roots add carbon to soil
what is special about AM and EM fungi
fungal symbionts and networks
mutualism
plants give fungus carbon
fungus gives plant nitrogen, phosphorus, and water
fungal network is so so so extensive and can bring nutrients to plants that they cannot reach on their own
fungus is within the root (not just on the outside) (infection adjacent)
what does “mineralize nitrogen” mean and why is it so important
microbes take up organic N and consume it, as long as they are carbon limited they will excrete carbon in mineral form
biotia MUST be limited by carbon because then they are consuming nitrogen in excess
what does it mean to say an organism is carbon limited, nitrogen limited, or phosphorus limited
limited = the material that they run out of first, plants need more of this to increase growth
plants tend to be nitrogen limited, microbes tend to be carbon limited
what are the aproximate C:N ratios of plants, soil organic matter, and soil biotia and under what conditions will soil biotia tend to mineralize nitrogen? are these conditions common or rare
25:1 is the ratio that changes from nitrogen limited (400:1 - 25:1) to carbon limited (25:1 - 10:1)
what are the major inputs and outputs of nitrogen to terrestrial ecosystems and how do those impact nitrogen availability over geological time
inputs: nitrogen fixing crops, nitrogen fixing bacteria, lightning
outputs: fertilizer, denitrification, mineral nitrogen
what are the major inputs and outputs of phosphorus to terrestrial ecosystems and how do those impact phosphorus availability over geological time
inputs: dust, weathering, fertilizer
outputs: occlusion
in terms of local recycling, are the nitrogen and phosphorus cycles similar or very different
very similar, just over different lengths of time
once inside an ecosystem, in what state does the typical nitrogen or phosphorus atom spend most of its time
nitrogen - organic nitrogen (months or years or decades)
phosphorus - organic phosphorus
once inside an ecosystem, what is the most common “circuit” that a nitrogen or phosphorus atom will travel
organic nitrogen gets decomposed by microbes, lives in microbes bodies for some time, nitrogen can be excreted by microbes, nitrogen is in mineral form (residence time=hours), is taken up by plants, which die/senesce and create organic nitrogen
what is immobilization of nitrogen or phosphorus
biotia that are nitrogen limited take up mineral nitrogen
nitrogen and phosphorus are unavailable for plants (in bodies of microbes)
from the standpoint of limitation by carbon, nitrogen, and phosphorus and its effect on nutrient cycling, are large animals similar to soil microbiomes or very different from soil microbiomes
very similar - 10:1 C:N ratio is very similar between humans and soil organisms
we are carbon limited like soil organisms
(more details, or just the information) why is decomposition so important to nitrogen and phosphorus cycling
when organic matter is decomposed, this becomes nitrogen for plants to absorb
does soil pH affect nutrient availability for plants? if so, what is the sweet spot
pH 6-8, pH makes it easier or harder for plants to take minerals up
organic pollutant intact and degrading processes in soils
intact: volatilization, leaching, runoff, capilary flow, absorption and exuidation
degrading: phodo decomposition, anaerobic degradation, aerobic degradation, chemical decomposition, detoxification
three ways that soil erosion typically occurs, what human activity is linked to soil erosion
water, wind, tillage
not a new problem, tilling makes it much more dramatic
what is thermophilic composting, what makes finished compost a useful soil amendment
large, well aerated piles of rapidly decomposing material
HEAT
three stage process, temperature gradually increases, increases by a lot (gets mixed), temperature falls and material is recolonized by organisms
what is biochar, what contributes to the huge diversity of properties of finished biochar? why is biochar useful as a soil amendment
heating organic materials with no air
different heat and materials contributes to a large diversity of biochar
positive impact on plant yields, enhances nutrients, plant growth
can remediate polluted soils
what observations about indigernous soil management practices in the very poor soils of the amazon led to the current biochar fever
burning waste in dirt pits and then covering them to smother the fire
what is manure and in what contexts can the carbon, microbes, and nutrients that manure contains be returned to the soil? in what contexts is that return cost prohibitive
animal poo, in small mixed farms manure can be a good source of minerals because it is easy to transport
when it is taken from CAFOs to agricultural farms, the cost is not worth it and the emissions negate the benefits
what are biosolids created by waste water treatment plants and how can they be used to improve degraded soils
when sewage is treated to meet certain standards of contamination
it can be spread on land to improve degraded soils
what are cover crops? why are they an important component in the management of healthy soils
crops rotated with cash crops to fertilize the land being used
increases biodiversity
its always healthy to have roots in the soil
what is phytoremediation and what are three ways that it can be used to stabilize or improve polluted soils?
phytoremediation - plants being used to remove municipal wastewater contaminants
phytostabalization.- any kind of plant is grown in order to stabalize the contaminant and reduce the spread
hyperaccumulation - plants can tolerate high levels of toxins, can safely remove the contaminant
enhanced rhizosphere phytodegredation - plants do not take up the contaminant, plant roots stimulate the growth of bacteria which degrade the contaminant
what were key takeaways from the “kiss the ground” documentary and how do they connect with class concepts
main point - soil in the context of climate change
CARBON !!!!!!
soils store so much carbon!
using regenerative (or less) agriculture we could store more carbon within the soil which could help to remove carbon from the soil
current practices are removing carbon from the soil and introducing it into the atmosphere (BAD)
