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
