5.4 Nutrient cycles Flashcards
What are saprobionts?
extracellular digesters that release mineral ions into the soil by feeding on dead and decaying matter
How do saprobionts digest DOM?
branching hyphae (mycellium) penetrate through the medium and secrete digestive enzymes and absorb the soluble products of digestion
What microorganism is the nitrogen cycle driven by?
bacteria - only cycle that is dependant on bacteria
What are all the chemicals of the N cycle?
N2 - nitrogen gas (very stable due to triple bond)
NH3 - ammonia (NH4+ - ammonium ions)
NO2- = nitrite
NO3- = nitrate
Why is N2 gas unavailable for most life?
it is very unreactive due to the stable triple bond
What ion do plants absorb in alkaline soils?
ammonium ions
What ion do plants absorb in acidic soils?
nitrate - NO3-
What are the 4 processes in the N cycle?
nitrogen fixing
ammonification
nitrification
denitrification
what is deamination?
amine group and hydrogen is removed from an amino acid - NH3
what is deamination?
amine group and hydrogen is removed - NH3
What is an example of deamination?
3.3 digestion - NH3 removed from an amino acid in the liver
What are nitrogen-fixing plants called?
legumes
What are nitrogen-fixing plants?
plants that have n-fixing bacteria growing in the root nodules
What is the nitrogen-fixing bacteria in the root nodules called?
rhysobium
How is nitrogen-fixing bacteria mutalistic bacteria?
plants get N compounds and bacteria gets C compounds such as glucose
How are N-fixing plants able to fix nitrogen (reaction)?
N2 —-> NH3
reduction reaction
enzyme = nitrogenase
What is the sequence of events of the N cycle starting from N2 in the atmosphere?
atmospheric pool of nitrogen —> nitrogen fixing N2 to NH3 can be taken up by plantsto make proteins (decomposition) —-> feeding - proteins in animals (decomposition) —> excetion = nitrogenous waste (urea) —> all decomposition contributes to DOM —> DOM and nitrogenous waste undergo ammonification = ammonia in soil (NH3) —-> nitrification = NO2- in soil —-> nitrification = NO3- in soil —> denitrification = N2 in atmosphere
What are the 2 nitrifying reactions?
both oxidation reactions:
1. NH3 —-> NO2-
2. NO2- —–> NO3-
What bacteria carries out ammonification?
saprobionts
What is the only process in the N cycle that has anerobic bacteria?
denitrification
Why do plants need nitrogen?
For ATP, nucleotides and amino acids synthesis
How can you identify plants that are living in nitrogen poor soils?
light green leaves and stunted growth
How does deforestation affect the nitrogen cycle?
leaving the stump = more DOM
soil quality decreases because N in soil is exposed to soil errosion and leeching
How does crop rotation improve soil fertility?
helps in restoring lots nutrients of the soil as the first crop plants use up all the nitrogen in the soil - farmers plant more legumes
How would large volumes of animal waste affecr the N cycle?
more organic matter produced for ammonification so more nitrates in the soil
How does using too much fertiliser affect the environment?
leeching of excess nitrates causes eutrophication
Why are aminals not essential for the N cycle?
plants also contribute to DOM for ammonification
How does harvesting crops affect the N cycle?
nitrogen is removed from soil by removing plants so reduces N recycling
Why is it necessary for farmers to plough their feilds?
minimises anerobic conditions and reduces denitrifying bacteria so increasing ammonification, nitrogen-fixing and nitrification
How do non-legumes obtain their nitrogen?
absorbs the NH4+ from the soil or the nitrate ions through their roots
What is phosphorus used for in plants?
synthesis of phospholipids, ATP and amino acids
How does Phosphorus naturally occur?
in mineral form as PO4 3- ions
Where are phosphate ions found?
sedimentary rocks
How do phosphate ions end up in the soil?
weathering of phosphate from rocks runoff as phosphate ions are dissolved in the water into soils
decomposition of plants and animals
How do plants absorb phosphate ions?
by active transport absrobed through the roots
How do phosphate ions end up in water bodies?
leeching
What happens when phosphate ions are in the water bodies?
phosphate is in solution
chemical precipiation occurs which causes sedmentaion to settle to the bottom to form new rocks causing geological uplifitng
What is the sequence of events of the phosphorus cycle starting from weathering?
phosphate ions in rocks —-> weathing of rocks causes runoff into the soil —-> plants take up phosphate ions —-> animals eat plants —-> plants and animals die —> more phosphates in soil —–> leeching into water bodies —-> phosphates in water body settle to the bottom as sedmentation —-> new rocks form —-> geological uplifting
What are the 4 roles of mycorrhizae?
- expand the nutrient absorption surface of plants
- increase absorption of phosphorus by plants
- enhance plant disease resistance
- aggregate soil and stimulate microbial activity
What is the mutalistic realtionship between mycorrhizae and the plant?
the plant has an increased SA to absorb more H2O and mineral ions
the fungi receives carbon compounds from the plant
What is the benefit of mycorrhizae expanding nutrient absorption surface?
competition for mineral ions and water limit root growth
the merrystems are soft tissue and if the soil texture is too rough it can limit root growth
roots with mycorrhizae can reach areas the roots cannot so inscreased absorption SA and range
How do mycorrhizae increase absorption of phosphorus?
the phosphorus cycle is unbalanced in terms of time due to geo uplifting
so when PO4 3- is available in the soil, plants absorb it very quickly leaving a phosphorus poor zone around the roots
with mycorrhizae - plants have more reach and can extend past the poor zone
What does aggregating soil mean?
binds the soil together
How does aggregating soil stimulate microbial activity?
binds the soil together = reduces soil errosion
stimulates microbial activity so the plant releases auxins which increases activites of other microbes in the soil overall improving the soil quality
When are fertilisers used?
for intensive food production when there is a high demand on the soil
in agricultural systems when nutrients in the soil decrease and productivity of plants is reduced
What are natural fertilisers?
fertilisers that contain DOM and contribute to the structure of the soil
What is the advantage of natural fertilisers?
releases nutrients gradually as it relys on saprobionts
decreases the liklihood of leeching as nutrients are not produced in excess
What are artificial fertilisers?
fertiliser made up from minerals that have been mined from rocks and provides a more conc source of minerals
What are the advantages of artifical fertilisers?
can be applied in smaller vol = more conc, so saves cost
can blend different minerals for particular crops
What are the overall advantages of using fertilisers?
replaces mineral ions removed in harvest
increases crop productivity
What are the overall disadvantages of using fertilisers?
replaces species diversity
leeching
eutrophication
How is plant productivity increased using fertilisers?
earlier growth
an increasing in SA for photosynthesis
so cheaper food is produced
How does using fertilisers reduce species diversity?
N rich soils favours grass which outcompetes other species
What is the problem with the relationship with saprobionts and nitrogenase?
bacteria are aerobes but nitogenase is inhibited by O2
What can be done to protect nitrogenase from O2?
it can live in an anerobic environment
generate a physical barrier around nitrogenase to prevent O2 diffusing into the enzyme
What 2 types of soil has anaerobic conditions?
waterlogged soils
compacted soils
What is done to reduce the anaerobic conditions of the soil?
ploughing and draining soils reduces anaerobic cond. so reduces denitrifying bacteria
Why does high conc of nitrate in soil cause crops to wilt?
lower water potential in soil = so potential grad in roots and water diffuses out of the plant into the soil by osmosis
What type of nitrogen conc soils to legumes live best in?
Nitrogen poor soils - they have nitrogen-fixing bacteria
How can digestive insects help plants grow in soil with low concentrations of nutrients?
Digestion/breakdown of proteins
Provides amino acids
Digestion/breakdown of named (organic) phosphate-containing compound e.g. DNA, RNA
Provides named (organic) phosphate-containing product e.g. nucleotides
Why do waterlogged soils have anaerobic conditions, with high concentrations of ammonium compounds and low concentrations of nitrates and nitrites?
Less nitrification
Less oxidation of ammonium ions to nitrite ions and nitrate ions
More denitrification – denitrifying bacteria are anaerobic
More nitrate ions converted to nitrogen gas
Suggest one way in which an increase in the uptake of phosphate could increase plant growth.
Used to produce named phosphate compound in cells; e.g. ATP / ADP / phospholipids / DNA / RNA
Describe the role of saprobionts in the nitrogen cycle.
(They use enzymes to) decompose proteins/DNA/RNA/urea
Producing/releasing ammonia/ammonium compounds/ammonium ions
how would crop rotation improve crop yield?
can grow plants with nitrifying bacteria
different crops use different mineral so they will be better suited to new areas with high concs of the minerals they need
Why would plants with nitrogen fixing bacteria grow more slowly than plants that get their nitrogen from fertilisers?
plants with nitrogen fixing bacteria need to use ATP to fix nitrogen
therefore there is less ATP avalaible for growth
