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The movement of nutrient elements through the various components of an ecosystem is called Nutrient cycling.

• Nutrient cycling is also called as Biogeochemical cycles (bio: living organism, geo: rocks, air, water).
• Standing State– Amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc., present in the soil at any given time. (Don’t get confused with standing crop)
• Nutrient cycles are of two types: (a) Gaseous and (b) Sedimentary.
• Gaseous nutrient cycle is Carbon cycle and nitrogen cycle. Reservoir for gaseous nutrient cycle exists in the atmosphere.
• Sedimentary nutrient cycle is Phosphorus cycle and Sulphur cycle. Reservoir is located in Earth’s crust.
• Rate of release of nutrients through cycles into the atmosphere is regulated by various environmental
  factors, e.g., soil, moisture, pH, temperature etc.

CARBON CYCLE

Simplified Carbon cycle

• Carbon constitutes 49 % of dry weight of organisms and is next to water.
• 71 % carbon is found dissolved in oceans. This oceanic reservoir regulates the amount of carbon dioxide in the atmosphere.
• Fossil fuels also represent a reservoir of carbon.
• Carbon cycling occurs through atmosphere, ocean and through living and dead organisms.
• Carbon is fixed in the biosphere through photosynthesis. A considerable amount of carbon returns to the atmosphere as CO2 through respiratory activities of the producers and consumers.
• Decomposers contribute to CO2 pool by processing of waste materials and dead organic matter of land or oceans.
• Some amount of the fixed carbon is lost to sediments and removed from circulation.
• Burning of wood, forest fire and combustion of organic matter, fossil fuel, volcanic activity are additional sources for releasing CO2 in the atmosphere.
• Human activities have significantly influenced the carbon cycle. Rapid deforestation and massive burning of fossil fuel for energy and transport have significantly increased the rate of release of carbon dioxide into the atmosphere, leading to greenhouse effect.

PHOSPHORUS CYCLE

Phosphorus is a major constituent of biological membranes, nucleic acids (DNA, RNA) and cellular energy transfer systems.

• Animals need large quantities of phosphorus to make shells, bones and teeth.

Phosphorus cycle in terrestrial ecosystem

• Rock is the natural reservoir of phosphorus, which contains phosphorus in the form of phosphates. When rocks are weathered, minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants.
• Herbivores and other animals obtain this element from plants. The waste products and the dead organisms are decomposed by phosphate-solubilising bacteria releasing phosphorus.
• Unlike carbon cycle, there is no respiratory release of phosphorus into atmosphere.
• Two major and important differences between carbon and phosphorus cycle are:

1. Atmospheric inputs of phosphorus through rainfall are much smaller than carbon inputs.
2. Gaseous exchange of phosphorus between organism and environment are negligible.