Wednesday, May 28, 2008

Cycling of nutrients

Standing state: The amount of nutrients such as C,N,P, Ca,etc.,present in the soil at any given time is known as standing crop.
• The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling or biogeochemical cycle.
• Types of Nutrient cycles- 1. Gaseous and 2. Sedimentary. The reservoir for gaseous type of nutrient cycle present in the atmosphere.

The reservoir for Sedimentary type of nutrient cycle present in the earth’s crust. Environmental factors such s soil, moisture, pH, temperature etc., regulate the rate of release of nutrients into the atmosphere.

· Carbon is essential component of all major organic compounds of protoplasm as carbohydrates, fats, proteins and nucleic acids.
· Carbon constitute 49% of the dry weight of the organisms and is next only to water
· In atmosphere .032% CO2 is present. out of the total quantity of global Carbon 71% Carbon is found dissolved in oceans
· CO2 is fixed in the biosphere by the process of photosynthesis by plants. The plans are able to fix carbon by the process of photosynthesis ranging from 4-9 x 1013 per year.
· Carbon fixed by producers enters the food chain and passed to herbivores, carnivores, decomposers.
· CO2 is released in atmosphere by respiration of producers and consumers.
· It is also released by the decomposition of waste materials and dead organic matter by decomposers in land or oceans
· Another source of CO2 is burning of wood, forest fire & combustion of organic matter fossil fuel. Volcanic activities are additional sources for releasing CO2 in the atmosphere.
· Some amount of fixed CO2 is lost to sediments and is removed from circulation. In oceans CO2 remains stored as bicarbonates as lime stone and marble rocks.
Phosphorous is the major constituent of biological membranes nucleic acid and cellular energy transfer systems (ATP). Many animals also need large quantities of this element to make shells, bones and teeth.
· The natural reservoir of phosphorous is rock which contains phosphorous in the form of phosphates.
· The inorganic phosphorous is added to the soil as a result of weathering of phosphate rock. It is absorbed by the roots of the plants.
· Herbivores and other animals take this element from plants.
· After death and decay of organisms phosphorous is recycled due to action of decomposers especially by phosphate - solubilising bacteria releasing phosphorous.
· Phosphorous cycle is different from carbon cycle in two ways :
o There is no respiratory release of phosphorous into atmosphere as in carbon cycle.
o Atmospheric inputs of phosphorous through rainfall are much smaller than carbon

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