Phosphorus, calcium and magnesium are components of the sedimentary cycle. Sulphur is to some extent intermediate, since two of its compounds hydrogen sulphide and sulphur dioxide formed under some circumstance, add a gaseous component to its normally sedimentary cycle. The elements concerned in the sedimentary cycle normally do not cycle through thermosphere but follow a basic pattern of flow through erosion, sedimentation, mountain building, volcanic activity and biological transport e.g., through the excreta of marine birds. The sulphur cycle is a good example to illustrate the linkage between air, water and the earth’s crust, and hence, a brief account of this cycle is given here.
Sulphur Cycle
Sulphur is found in gaseous forms like hydrogen sulphide and sulphur dioxide in the atmosphere, and as sulphates, sulphides and organic sulphur in the soil. The only known natural source of above gases in the atmosphere is volcanic emission. Nowadays, from burning of fossil fuels, sulphur is released in the atmosphere at a rate that is expected to equal the emission from natural sources by the year 2000 AD.
Sulphur is an essential constituent of certain amino acids, and vitamins of the B-complex group. Sulphur I the form of sulphates is incorporated in the proteins of autotroph tissues. It then passes through the grazing food chaining and excess of it is released through the faeces of animals. Within the detritus food chain, the decomposition of proteins releases sulphur. Under aerobic conditions fungi like Aspergillums and Neurospora and under anaerobic conditions the bacterial like Escherichia and Proteus are largely responsible for the decomposition of proteins.
ADVERTISEMENTS:
In anaerobic soils and sediments, hydrogen sulphide is formed by sulphate reducing bacteria like Desulphoyibro desulfuricans. Species of Beggiatoa oxidize hydrogen sulphide to elemental sulphur and species of Thiobacillus oxidize it to sulphate. There are also green and purple sulphur photosynthetic bacterial that oxidizes hydrogen sulphide to elemental sulphur.
Now that you have learnt how organisms depend on the environment for their energy and material requirements, we will examine the relationships between organisms of the same species and among organisms of different species. We will start at the population level, the level of interaction among members of the same species.