Primary Productivity
All life on earth depends on the production of new organic matter within ecosystems. The earth's organisms either produce their own food or consume it after others have made it. The organisms responsible for primary production are known as primary producers or autotrophs (self-feeders). They form the base of the food chain, and using chlorophyll they alone are able to capture and store energy from the sun through photosynthesis.
Various ecosystems differ in their primary productivity. This is significant as it determines the food supply for humans and other animals.
Various ecosystems differ in their primary productivity. This is significant as it determines the food supply for humans and other animals.
Gross Primary Productivity
Gross Primary Productivity (GPP) is the rate at which the primary producers in an ecosystem convert the sun's energy into chemical energy. GPP is measured in terms of the energy produced per unit of area over a given time span, such as kilocalories per square metre per year.
The diagram above shows satellite data of the earth's GPP in terms of ocean and land concentrations of chlorophyll. It can be seen that the tropical rainforest areas around the equator have high chlorophyll concentrations.
Net Primary Productivity
Not all of the chemical energy produced by primary producers through photosynthesis is available to other organisms in an ecosystem because the producers must use some of it for their own respiration in order to stay alive, grow and reproduce.
Net Primary Productivity (NPP) is the rate at which producers use photosynthesis to produce and store chemical energy minus the rate at which they use some of this for their own respiration. The highest NPP rates are in swamps and marshes, tropical rainforests and estuaries, while the lowest are found in the desert, tundra and open ocean.
Net Primary Productivity (NPP) is the rate at which producers use photosynthesis to produce and store chemical energy minus the rate at which they use some of this for their own respiration. The highest NPP rates are in swamps and marshes, tropical rainforests and estuaries, while the lowest are found in the desert, tundra and open ocean.