Net Primary Productivity

Net Primary Productivity Definition

Net Primary Productivity or NPP can be defined as the rate of accumulation of biomass or energy. The energy utilised during metabolic processes such as respiration is excluded from gross productivity (GPP).

NPP is calculated primarily by an increase in the biomass in a unit time per unit area.

• Organic matters are synthesised by plants by the process of photosynthesis. In the process, light energy is converted to chemical energy and stored in the plant cells. It is available for the consumption by the organisms of the next trophic level
• Autotrophs or primary producers are responsible to trap solar energy
• Carbon dioxide and water are used to form carbohydrates, which are stored
• All the energy absorbed does not account for organic matter formed. A quarter of the amount absorbed is utilised for various biological processes
• Net primary productivity excludes these losses and is calculated by only taking the resultant organic matter, which is transferred to the food web
• NPP = GPP – Energy loss due to respiration by plants
• NPP is calculated in mass per unit area in unit time
• Net primary productivity is dependent on various factors such as temperature, nutrient availability, humidity, sunlight, etc. present in an ecosystem
• NPP is highest in tropical forests and lowest in deserts
• Around 1% of the total solar energy reaching the earth per unit area and time gets stored in the form of biomass

Gross Primary Productivity and Net Primary Productivity

Productivity refers to the rate of energy or biomass or organic matter is added. The productivity of primary producers is referred to as primary productivity.
 
Primary productivity is of two types: gross primary productivity (GPP) and net primary productivity (NPP).
 
Gross primary productivity (GPP) is the rate at which solar energy is captured per unit area in a unit time during photosynthesis.
 
Some of the energy captured is utilised in metabolic processes such as respiration, growth and maintenance so the NPP is calculated by excluding these from GPP.
 
So the net primary productivity is the rate of energy storage, which can be transferred to the consumers.

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