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Phosphorus Cycle

Phosphorus Cycle


• Phosphorus is used primarily in ATP production
• The main source for phosphorus occurs from mineral ions
• Phosphorus exists primarily as PO43- ions in the form of sedimentary rock deposits
• Dissolved rocks allow the phosphorus to be released for absorption by plants
• Animals get their phosphorus from consuming the plant
• Excess phosphate ions are excreted by animals and may accumulate in waster material
• Dead plants and animals are decomposed using bacteria/fungi which releases the phosphate back into the soil/water
o Phosphate remains in bones and therefore is trapped
• Phosphate ions in excreta released by decomposition and dissolved out of rocks are transported by streams and rivers into lakes and oceans where they form sedimentary rocks

Nitrogen Cycle

Nitrogen Cycle

• Nitrogen is required for the production of nucleic acids, proteins, amino acids etc
• Despite the high content of nitrogen in the air (~78%) it is too stable for it to be used directly
• Plants uptake nitrogen through nitrate ions (NO3-) from the soil through active transport. It is here that nitrogen is then entered into the food chain as consumers then digest the plant and thus obtain its nitrogen.
• Nitrate ions are very soluble and are added into the soil greatly by the decomposition of plants and animal matter. It is also added in fertilisers
• Nitrate ions must be in aqueous conditions to enter the xylem vessels by the root hair cells of the plants


Ammonification
• Production of ammonia from organic ammonium containing compounds
• Ammonification usually occurs in the production of Urea (which contains a high concentration of amino acids), proteins, nucleic acid and vitamins ( found in faeces and dead organisms)
• Saprobiotic microorganisms (greatly fungi and bacteria) feed on the material and thus release the ammonia which later form ammonium ions in the soil
• It is through ammonification does nitrogen return back to the non-living component of the ecosystem

Nitrification
• Nitrification is the product of nitrifying bacteria chemical reaction to produce energy.
• However, in doing so do they convert ammonium ions into nitrate ions in an oxidation reaction
• The oxidation reaction is a two stage reaction:
1) Oxidation of ammonium ions to nitrite ions (NO2-)
2) Oxidation of nitrite ions to nitrate ions (NO3-)
• Nitrifying bacteria are aerobic, and therefore require oxygen to be present within the soil, hence why ploughing is important to ensure the soil is aerated. Good drainage is also required to ensure water does not fill spaces and prevent air being forced out of the soil
Nitrogen Fixation
• Nitrogen gas is converted into nitrogen containing compounds.
• It can be produced industrially as well as naturally through lightning passing through the atmosphere
• However, the most significant form of nitrogen fixation is through microogranisms:
o Free-living Nitrogen Fixing Bacteria: bacteria which reduce gaseous nitrogen into ammonia. The ammonia is then used to produce amino acids. Nitrogen rich compounds are released from these when they die and decay.
o Mutualistic Nitrogen Fixing Bacteria: Bacteria which live in nodules on the roots of plants, such as peas and beans, they obtain carbohydrates from the plant in exchange for amino acids from the bacteria
Denitrification
• When soil becomes waterlogged and thus there are anaerobic conditions the nitrifying bacteria, which are aerobic, cannot function and there is thus an increase in anaerobic denitrifying bacteria
• Denitrifying bacteria convert soil nitrates into gaseous nitrogen
• Ultimately, this reduces the availability of nitrogen containing compounds for plants

Fertilisers

Fertilisers

Fertilisers are required in farming as nitrogen is naturally restored back into the soils in farmland
Natural (Organic):
• Consist of dead and decaying remains of plants and animals as well as animal wastes such as manure or bone meal
Artificial (inorganic):
• Mined from rocks and deposits and then converted into different forms and blended together to give the appropriate balance of minerals for a particular crop.
• Compounds containing nitrogen, phosphorus and potassium are almost always present
Effect of Nitrogen Fertilisers
• Nitrogen is required in the production of amino acids and therefore required in plants – especially in the leaves which are the site of photosynthesis. The increased amount of photosynthesis in the leaves is directly correlat4ed to the crop’s productivity.
• However there have been consequences using nitrogen fertilisers:
o Reduced Species Diversity:
Nitrogen rich soil favours growth of fast-growing species such as grasses and nettles. However, the result is less resources for other species ultimately resulting in death.
o Leaching:
Leaching is the removal of nutrients from soil as a result of rain water. The nutrient, such as nitrates, are dissolved into the rain water, and carry them deeper into the soil where plant roots are unable to get hold of them. The nutrient rich water finds itself way into watercourses (i.e. streams and rivers) which may result in it running into freshwater lakes.

The side effects of drinking nitrate rich water can lead to poor oxygen association in babies and stomach cancer in adults. The leached nitrates can also cause eutrophication.
o Eutrophication
Eutrophication is the process in which nutrient build up in bodies of water.
1) Naturally, there is a low concentration of Nitrates in lakes and rivers. Nitrates are a limiting factor for plant and algal growth
2) An increase in nitrate concentration results as a result of Leaching, results in the limiting factor of nitrates to be removed, therefore the algal and plants from exponentially
3) As algae grow on the water surface, there is a high population of algae there, known as an ‘algae bloom’. The dense layer of algae results in light being absorbed and therefore unable to reach a greater depth
4) Light becomes the limiting factor for the growth of plants and algae at lower depths and thus they eventually die
5) The high abundance of dead plant and algae matter means that there is no longer a limiting factor for saprobiotic algae and therefore it too can grow exponentially using the dead organisms as food.
6) Saprobiotic bacteria are aerobic, and thus there is a higher demand for oxygen. Therefore, the concentration of oxygen is reduced and nitrates are released from decaying matter
7) Oxygen becomes the limiting factor for the population of aerobic organisms, such as fish – ultimately leading to their death
8) Without aerobic organisms, these is less competition for the anaerobic organisms, whose populations now rise exponentially
9) Anaerobic organisms further decompose dead matter, releasing more nitrates and some toxic wastes, such as H2S, into the water resulting in the water becoming putrid.