Primary Production - Ecosystem

Energy accumulated by plants during photosynthesis is called production or more specifically primary production. It is the first and the basic form of energy stored in an ecosystem. Production is defined technically as the amount of biomass or organic matter produced per unit &ea in a given period. It can be expressed in terms of 2 weight (g/m²) or energy {kcal/m).

The rate at which energy accumulates is  known as primary productivity. It is expressed in terms of kcal/m /yr or g/m²/yr. In case of plants, primary production is generally differentiated into two distinct categories, namely gross primary production (GPP) and net primary production (NPP). Gross primary production refers to the total amount of solar energy fixed into organic matter by primary producers through photosynthesis. A considerable portion of the solar energy fixed by plants (GPPI. is utilised by plants themselves in respiration (R) to get the energy needed for their metabolism and for other vital functions. The amount of energy left after respiratory consumption (R) is incorporated into new body tissue (growth) or is used for producing new individuals (reproduction). The amount of biomass or organic matter accumulated by plants per unit area in a given period is called net primary production. The overall relationship between GPP and NPP can be written as:

GPP - R = NPP or GPP = NPP + R

From this equation you might have noticed  that whatever  energy is fixed by plants (GPP) some of  it  is used  for their own maintenance  (R) and only remaining  (NPP) is  available for the next trophic  level.  So net primary production is the only energy available for the next trophic level.