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Productivity of an Ecosystem

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Productivity of an Ecosystem - Lesson Summary

Biomass is the mass of living organisms or the organic matter in a unit area of an ecosystem at a given time.  The amount of biomass varies from one ecosystem to another. It is expressed in terms of mass per unit area. If we compare a forest, desert or tundra ecosystem, we find that the biomass of the forest ecosystem is greater than the other two. This is due to the presence of a large number of primary producers in the forest. During photosynthesis, plants use chlorophyll to fix inorganic substances such as water and carbon dioxide into organic substances such as glucose in the presence of sunlight, which acts as the main source of energy. So the light energy of the sun is converted into chemical energy of glucose or sugars. Therefore the amount of biomass produced per unit area by plants through photosynthesis is called primary production. The rate of primary production is called primary productivity.
The primary productivity of an ecosystem is dependent on the plant species inhabiting the area and several other factors such as the photosynthetic capacity of plants and availability of nutrients. As a result, it varies from one ecosystem to another. Primary productivity can be categorised as: gross primary productivity and net primary productivity. GPP is the total energy fixed by primary producers as biomass through photosynthetic activity per unit area per unit time. A fraction of this GPP is used by plants during respiration to meet their energy requirements. This is known as respiration losses and is denoted as ‘R’. Now, if respiration losses are subtracted from GPP, Net Primary Productivity is btained, which is the net biomass available for consumption by heterotrophs. Heterotrophs such as herbivores, carnivores, omnivores and decomposers feed on this net biomass available either directly or indirectly and convert chemical energy of their food into their own biomass. The rate of formation of biomass by consumers called secondary productivity. The food or energy assimilated and stored by autotrophs is passed on to the consumers, which further transfers it to next trophic level. The efficiency with which this energy transfer takes place from one trophic level to the other is called energy efficiency.
The least productive ecosystems are the ones limited by sunlight and water while the most productive ecosystems are the ones with high temperatures, plenty of water and nutrients. In this manner, productivity is vital for the production of biomass in any ecosystem.

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