(a) Primary productivity is defined as the amount of biomass or organic matter produced per unit area over a time period by
plants during photosynthesis. The rate of biomass production is called primary productivity.
It is expressed in terms of g−2yr−1
where g = weight
Or(kcal m−2)yr−1
(b) Gross primary productivity (GPP) 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).