midterm Flashcards
observations of spodosol from week 1
the top looks more freshly decomposed/was still decomposing
lots of sticks and leaves at the top
lighter and sandier at the bottom, more roots
sandier section is crumbly and breaks away easily
top of the sample was spongey
very abrupt change between leaves and sticks to dirt (horizons)
saw an ant! (and other insects)
fungi –> mycelium (body) –> hyphae (makes up mycelium)
fresh plant - wintergreen/blueberries
burnt bits of wood –> evidence of fires
4 earth domains that come together in soil - how are they present?
minerals (rock), (air), water , biota (living things)
major components of soil and their approximate proportions
mineral matter (45%), air (25%), water (20%), organic matter (7%), biota (3%)
three soil mineral particle sizes (impact on soil surface area, pore size, water holding capacity) and what is different about them (surface charge, primary vs secondary), consequences of the differences
sand (largest), silt (medium), clay (small)
clay has a lot of surface area because it is small
clay is negatively charged so that positively charged nutrient ions can stick
pores are filled with air, water, and biota
clay soil has smaller pores
larger pores will release water easier, smaller pores will hold on tighter to more water
larger pores hold more air
physical and ecological significance of soil pore space - what is different about marcopores
pores contain air, water, and biota which are essential for soil life
provides oxygen to aerobic organisms
in smaller pores it is harder for plants to remove water
does “healthy” soil have a diversity or uniformity of pore size, and why is that healthy
the best soil is made up of many different parts which would create a large amount of diversity which is healthy because different types of plants can take what it needs from the soil, impacts how roots move through soil - diversity helps that happen
wanting a good mix of air and water - needs a diversity of pore sizes to achieve this
equal parts water and air
what are the causes and consequences of soil compaction
a reduction in pore space caused by vehicle traffic among other things
can impact farm yield
figure 4.8 in chapin text
the percentage of soil volume that is made up of water and how if affects the available water in soil depending on the different soil types
taxa of soil organisms responsible for ~95% of terrestrial decomposition and ecological advantages or disadvantages of each taxa
fungi and bacteria are responsible for ~95% of decomposition
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
soil animals - fragment transform and transport litter,
why do bacteria produce biofilms and 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
bacteria can go into a state of being alive, but metabolically they arent
living but expending no energy - can still respond from queues from the world and then revive
results from a lack of nutrients in the soil to support active life
can be extreme - can survive a lot more in their dormant state
main ecological roles of soil microfauna, mesofauna, and macrofauna - effects on decomposition
microfauna - less than .1 mm in diameter - nematodes and protozoans
protozoans are predators in the rhizosphere (eat fungi, bacteria, and plants), reduce bacterial:fungal relations, bacterial (and fungal) population is influenced which impacts population structures of other decomposition population
mesofauna - between .1 and 2 mm in diameter, greatest effect on decomposition, alters the microbial communities
macrofauna - ecosystem engineers, modifiy the physical properties of soils and litter, creates pattern in soil structure
in which “earth” domain are soil bacteria and microfauna found in
mainly found in water
importance of the rhizosphere
plants exude things into the soil, hot spots of biological activity - lots of bacteria and protozoa
major classes of organic materials present in soils - which are labile carbon and which are soil humus, what are the distinctions
labile carbon - rapid turnover, living organic biomass, identifiable dead tissue, free bits of partially-degraded tissue, free or dissolved biomolecules
humus - slow turnover, protected bits of degraded cell walls and tissue, protected biomolecules, supramolecules, and degradation products, 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 - materials can be stuck inside
DISTINCTIONS
protected vs unprotected materials
labile (unprotected) - fungi and bacteria exude enzymes which break down plant litter which creates dissolved organic carbon which is absorbed by the fungi and bacteria again
