Difference Between Gross Primary Production (GPP) and Net Primary Production (NPP)

Gross Primary Production (GPP) vs Net Primary Production (NPP)

Even though earth is a closed system for materials and nutrients, it is an open system for the energy. Primary production is the process which inorganic compounds such as water and carbon dioxide are converted into organic compounds through living organisms using an energy source. Although the main energy source is sunlight, some organisms use chemical energy to produce organic compounds.

The process that uses sun light as the energy source to produce organic compounds is called photosynthesis. Organisms that involve in photosynthesis are known as autotrophs or primary producers. Some organisms use chemical energy from the oxidation or reduction of chemical compounds as the energy source, so they are called lithotrophic organisms. Portion of the fixed energy is used to internal processes such as respiration and photorespiration (Taylor, 1998).

However, in the primary production process, complex organic compounds such as carbohydrate are synthesized from simple inorganic compounds. The fixed energy flows through food chains to consumers who are heterotrophs.

As the latitude earth surface varies, total fixation of energy may also differ from location to location, and different locations vary with the amount of vegetation. Some energy is lost due to the reflection, radiation, and heat of the evaporation. So, primary production varies spatially and temporally.

However, this is an important phenomenon to determine the total energy flow through the living organisms and determination of biomass production.

Gross Primary Production (GPP)

Gross primary production is the total energy fixed as organic compounds including energy used for the respiration. Further explaining, gross production is the total carbon dioxide fixed by autotrophs per unit of time . So, it includes the energy fixed by photoautotrophs and chemoutotrophs. Unit of the GPP is Maas/Area/Time.

GPP can be theoretically calculated since all inorganic components are converted into organic compounds; i.e. sugar. So by measuring sugar, GPP can be calculated.

Net Primary Production (NPP)

Net primary production is the energy fixed as organic compounds or total biomass excluding the energy used for respiration. This is the potential available energy for the next level. So, this NPP is used to maintain the plant processes and food for consumers. Unit of the NPP is the same as GPP; i.e. Maas/Area/Time.

What is the difference between Gross Primary Production (GPP) and Net Primary Production (NPP)?

• The main difference between GPP and NPP is that gross primary production is the total energy fixed as organic compounds including energy used for the respiration, whereas the net primary production is the energy fixed as organic compounds or total biomass excluding the energy used for respiration.

• GPP is difficult to calculate because it is hard to accurately determine the energy used for metabolic processes such as respiration, as it is an ongoing process, whereas NPP is easy to calculate because it excludes respiration.

• GPP is measured during night using Eddy covariance system, since it measures respiration of biotic objects of the ecosystem, whereas NPP doesn’t need that calculation since respiration of plant is excluded .

• Measurement of NPP is generally used in terrestrial systems than GPP since accuracy is low .

Reference

Taylor, D.J., Green N.P.O., Stout, G.W., (1998), Biological Science. Cambridge University Press, Cambridge