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Flashcards in the living soil Deck (44)
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what is a lichen

symbiotic relationship between algae and fungi and sometimes cyanobacteria


what does algae provide to the lichen

it fixes CO2 (photosynthesis) which is a food source for the fungus


what does fungus provide to the lichen

it protects the algae and releases organic acids that accelerates mineral weathering


what does the cyanobacteria provide to the fungus

it fixes nitrogen


what is the early role of lichens in soil formation?

generally are the initial colonisers as they are capable of both photosynthesis and nitrogen fixation


where would you find bacteria in an aggregate

in the water filled pores or surrounded by a film of water on the walls of air filled pores and forming colonies


where would you find fungi in an aggregate

same places as bacteria but also in unsaturated pores


why don't microbes live in all pores

- size determines what microbes can fit as the pore necks may be to small to get into
- size also determines the level of saturation generally thus small pores are normally saturated (anoxic) which means only anearobes can occupy them and large pores often unsaturated so only areobes can live in the and microbes like bacteria will dry out.


why do bacteria prefer pores only slightly larger than themselves

- protects them from larger predators and prevents them from drying out


how does a pore full of water affect microbe metabolism

- oxygen diffusion is much slower in water thus the middle of the pore would be anoxic and you would only find anaerobes present and the outer areas would have better oxygen diffusion


how does soil orgainic matter influence aggregation

helps to bind soil particles together and inceases water holding capacity
increased OM = increased microbial activity as they feed on it


distribution of microbes within the soil profile are driven by ...

- the amount of om which decreases with depth
- the presence of the water table - oxygen requirements


where are protozoa predominately found in the soil profile

- in the rhizosphere (soil region immediately under the influence of roots )


where is algae commonly found in the soil profile

- they need access to light for photosynthesis so are only really found in the root zone


where are anearobic/ areobic bacteria found and what influences their presence

- presence of a water table will affect where these microbes are found
- but both can be found at the same depth as access to oxygen varies widely across an aggregate


why does the cation exchange capacity of straw residue increase over time

molecules become smaller and smaller and oxidised so the become water soluble and able to easily react with minerals


what microbes are primarily responsible for the decomposition of lignin

- white rot fungi which can decompose lignin to CO2 and H2O
- the lock an key method doesn't work however as lignin is not formed by uniform structure


what are the chemical and physical protecting mechanism of OM in soils

- physical - only occurs in micropores where the pore neck is to small for the microbes to enter
- chemical = interaction with amino surface so microbes will have to use more energy to break these bonds before they can start decomposing so if there is om nearby that is in a chemical bonds microbes would prefer to expend less energy and decompose that om instead


how does the tokumaru silt loam protect Organic matter

physical = high as there will be a presence of micropores
chemical = dominant in clay so will have some chemical protection (energy requirement to break bonds) but its is a pallic soil so it drains poorly and loses iron oxide which are important for the chemical protection


how well does the Waitere sandy soils protect OM

physical = low due to the high presence of macropores thus the pore necks will be large enough for microbes to enter
chemical = low as there is no charge so the inorganic compounds that bond to OM to protect is won't be so present as they would be in a clay soil


how well doe the egmount silt loam + allophane soil protect OM

Physical = due to presence of micropores and the chemical properties also help to increase presence of micro aggregates
chemical = high as there is the inorganic compound of allophane present which om can bond to


describe the process of nitrification
- requirements for this to take place
- where it would take place

is the conversion of ammonium (NH4+) to Nitrite (NO2-) by nitrosomonas during this nitrous oxide (bad green house gas) is released then by nitrobactor nitrite is converted to nitrate (NO3-)
- require oxygen, optimum temp, moisture and non acdic environment to take place
- thus in the outer zone of a soil aggregate as oxygen is needed


describe the process of denitrification
- requirements
- where it would take place in an aggregate

it is the conversion of Nitrate (NO3-) to nitrous oxide (N2O) then too Nitrogen gas (N2)
- this happens when the environment is anoxic as it forces microbes to use the nitrate for respiration instead of oxygen - flaculative anaerobes are responsible so if there is presence of O2 denitrification wont happen
- so would happen in the inner part of a soil aggregate


what issues arise with the denitrification process

- if the process doesn't complete fully ie oxygen is introduced more nitrous oxide will be produced which is a harmful green house gas


leaching is one way nitrogen is lost from the soil how does this occur

if the nitrate is not take up by the plants and left in the soil and rainfall comes it will then be leached


ammonia volatilisation is a way nitrogen is lost from the soil explain how this happens

NH4+ is converted to NH3+ through an equilibrium equation (NH3+ + h2o = NH4+ + OH-) if ph increases say with the application of urea the reactions will shift to the left and ammonia will be released


what are the four ways organic N can be lost from the soil and how is it converted to NH4+ for these processes to happen

- organic n is converted to NH4+ by enzymes breaking the amine group bonds
1. ammonia volitilsation
2. nitrification ( production of nitrous oxide)
3. leaching
4. denitrification


if the C:N ratio is higher than 30 what will happen

- net immobilisation will take place as all the N will be used up for microbial biomass growth and although there will be left over C there is insufficent N for the decomposition process to continue unless mineral N (NH4+ or Nitrate) is taken up from the soil


what is the implications of a high C:N ratio for farmers?

- lead to competition between the microbes and plants leading to a deficiency in plants = poor growth and yellowing.


if the C:N ration is below 20 what will happen

- net mineralisation as there will be N left over after microbes have used it for growth