Iasscore:: Biogeochemical Cycling/Nutrient Cycling

Biogeochemical Cycling/Nutrient Cycling

Nutrients or minerals are transferred from air, water and soil to producers to herbivores to carnivores to decomposers and finally to air, water and soil. Thus nutrient flow is bidirectional or cyclic and continuous in nature.

Sulphur Cycle

• Sulphur (S) forms linkages between the polypeptide chains which combine together to form protein. It helps in protein synthesis. 

• Sulphur exists in several oxidation states in nature: H2S, SO2-, SO4-2. Sulphur exists in elemental form also.

• Important steps of sulphur cycle are as follows:

a) Sulphur is also locked in coal and petroleum and released as SO2 when burned.

b) Suphite ions convert into sulphate ions in solution form. Plants absorb sulphates from soil and water.

c) Bacteria decompose the dead and decaying parts of plants and animals. H2S is released in the bacterial decomposition.

d) H2S is converted to SO4 by bacteria of genus thiobacillus, which is absorbed by plants (Nutrient).

Carbon Cycle

• Carbon forms the major components of the organic matter i.e. plant, animal body.

• CO2 is present in earth’s atmosphere (0.035 per cent).

• During the process of carbon fixation, carbon dioxide is taken up from the atmospheric reservoir (or from bio carbonates dissolved in water) by plants, photosynthetic bacteria, and algae and is "fixed" into organic substances. 

• Animals obtain their requirements for carbon (as carbon-based molecules) by eating plants or other animals. 

• For the biological links, the carbon cycle comes full cycle when carbon is released by either plants or animals as they respire or after life as they decompose.

• Organisms respire carbon dioxide as a waste product from the breakdown of organic molecules as their cells derive energy from oxidizing the molecules containing "fixed" carbon. 

• The burning of organic material such as wood or fuels also results in the release of carbon dioxide from organic carbon.

Nitrogen Cycle 

• Nitrogen is the essential macro-nutrient (required in large amount) for the plant and animal growth. The major amount of nitrogen is gaseous and thus present in atmosphere. Pants cannot absorb the gas. Thus it is converted to some other absorbable form by nature.

• The process of converting atmosphere nitrogen to the forms which plants can absorb is known Nitrogen Fixation.

• Atmospheric nitrogen can undergo nitrogen fixation by lighting and UV radiation and become NO3-.

• Biological/biotic N-Fixation occur by certain micro-organisms: as Rhizobium , Azotobacter, Clostridium, Anabaena and Nostoc.

• Following nitrogen fixation, nitrification occurs. During nitrification, ammonia is converted into nitrite, and nitrite is converted into nitrate. 

• In the final stage, plants absorb ammonia and nitrate and incorporate it into their metabolic pathways. 

• Nitrogen is released back into the cycle when denitrifying bacteria convert NO3- into N2 in the process of denitrification, when detrivorous bacteria convert organic compounds back into ammonia in the process of ammonification, or when animals excrete ammonia, urea, or uric acid.