The amount of biomass or organic matter produced unit area over a time period by plants during photosynthesis . The rate of biomass production is called productivity. Unit - weight (g-2) or energy (Kcal`m^(-2))`. Gross primary of an ecosystem is the rate of production of organic matter during photosynthesis. Net primary productivity is the available biomass for the consumption ot heterotrophs.
GPP-R=NPP
