Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis . It is expressed in terms os g -2 yr-1 od r (Kcal m-2 ) Yr-1 to compare the productivity of different ecosystems . it can be divided into gross primary productivity (GPP) and net primary productivity (NPP) . Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration .Gross primary productivity minus respiration losses (R ) is the net primary productivity (NPP). ltbrlt GPP-R=NPP
Net primary productivity is the available biomass for the consumption to heterophs.
