Biogeochem - Phosphorus cycle Flashcards
Is phosphorus a macronutrient, micronutrient or both?
both
what is the connection between water pollution and phosphorus?
increase in phosphorus levels increases the growth rate of phytoplankton and algae, causing algal blooms which removes the oxygen from the water system, causing water degradation
phosphorus role in cells?
Backbone of all nucleic acids
DNA
- 2 strands
RNA
- single strand
Phospholipid bilayer
- Polar heads and hydrophobic tails
ATP and ADP
how Adenosine triphosphate (ATP) converting to ADP release energy?
the breaking of the phosphate bond releases energy which is used for doing work
What happens when phosphorus is discharged in large quantities into the environment ?
life becomes more productive… ie
- alae, phytoplankton, cyanobacteria use it to increase rates of photosynthesis
Why does the environment degrade when phosphorus is released into the environment
lots of organic matter is produced which is then oxidised by organisms consuming the oxygen, leading to deoxygenation within the water body
Why is phosphorus a biolimiting nutrient?
because its availability restricts the growth of organisms and the productivity in ecosystems
What is the link between phosphorous and O2 levels in the atmosphere
volumes of phosphorus in the oceans in the early earth was low until volcanic activity and the movement of tectonic plates started occurring
this released phosphorus trapped in the rocks in to the seawater which photosynthetic organisms could consume and photosynthesise to produce oxygen and organic carbon
what is the dominant form of phosphorus in the evnironment?
Phosphate (5+)
phosphorus assimilation into biomass
- nucleic acids
- phospholipids in cell membrane
- energy (ATP)
- bones in vertebrates
forms of phosphorus in the environment
- Phosphate (+5)
- Phosphite (+3, rare)
- Hypophosphite (+1, rare)
What do high levels of phosphorus in the environment signify?
lots of DNA synthesis is occurring, meaning high levels of growth, reproduction
theres lots of recycling phosphorus into cells
what do low levels of phosphorus in the environment signify?
there is more internal cycling of P in the environment.
Cells are trying to preserve the phosphorus by intracellular cycling. The cell adapts how it assimilates phosphorus depending on how much is available in the environment
In acidic conditions, what form of P is commonly found?
P compounds which have formed with hydrogen
Phosphoric Acid
what is the typical pH in marine systems
8
What form is phosphorus present in at pH 8 in marine enviornments?
HPO42-
Hydrogen phosphate
Why is phosphorus present as HPO42- in marine environments
The acidity of the environment impacts the form in which Phosphorus is present. This is due to the dissociation constant pKa and redox reactions.
In oxic environments, phosphorus gets bound to iron(III), making it not bioavailable to organisms to use. This leads to phosphate having the the potential to be buried in the sediment. In anoxic conditions, iron(III) is reduced to iron(II), releasing phosphate.
The form in which is it appears id dependent on the pH value. As marine environments are ~ pH 8, phosphorus is present as hydrogen phosphate HPO42-, whereas in acidic conditions, due to the increase in hydrogen ions, the compounds formed will obtain more hydrogen, hence H3PO4 is the common form in acidic conditions.
Factors limiting phosphate uptake in cells
- bound to rock minerals
- bound to detrital minerals
- competition between arsenic or phosphate
Methods in which P is taken up into cells
- taken up as PME (phosphate monoesters)
- taken up at PDE (phosphate diesters)
- mycorrhizal fungal association
how is phosphate taken up into cells through phosphate transportation
(hint: affinity)
Low affinity phosphate transportation
- allows phosphate to migrate into cells at any time
- this only works when there is lots of P in the environment
High affinity phosphate transportation
- they can take small amounts of phosphorus into the cell
- is there is competition with arsenate, they can distinguish between P and As and just take up P.
What is alkaline phosphatase?
An enzyme that the cell produces which gets released into the environment and binds to phosphorus which assimilates into it
How do iron oxides act as a source and a sink of P in the environment?
In the water column (in oxic conditions) iron is found in its oxidised form, Fe(III) which has a high affinity to phosphate. This means that phosphate gets bound to Fe(III) which gets buried in sediments, providing a sink for P.
When the Fe(III) gets buried, in the sediment profile, oxygen is consumed which turns the conditions anoxic. When the iron reaches the iron reduction layer, due to the anoxic conditions, Fe(III) gets reduced by iron-reducing bacteria to Fe(II), aided by the spare electrons from organic matter degradation. This causes P to be released into the sediment column, indicating that iron oxides can also be a sink.
What is formed when P levels become saturated in the sediment column?
Apatite can be formed in the sediments which is a carbonate form of phosphate.
How did the snowball glaciation cause an increase in phosphate levels in marine sediments and thus marine life?
as the glaciers were melting, the ice ‘churned’ up the rocks, causing mechanical weathering to occur. This caused an increase in clay minerals which acted as surfaces which phosphorus could attach to and was transported into the seawater.
due to the pH of seawater, is dissociated and became bioavailable. This presence triggered of animals and photosynthetic cyanobacteria.
This started producing oxygen and food (organic matter), increasing the marine life numbers
