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).
GPP=NPP+RorGPP−R=NPP
The Net primary productivity (NPP) is the available biomass for the consumption to heterotroph (herbivores and decomposers).