5.9—GPP, NPP and plant respiration

Gross primary productivity (GPP) is the rate at which producers store chemical energy during photosynthesis. Net primary productivity (NPP) is what remains in new plant biomass after respiratory losses: NPP = GPP − R.

Match each value to GPP, NPP or R before calculating, keep area/volume and time units consistent, and rearrange the equation when the unknown is GPP or R.

If GPP is 17,500 kJ m⁻² yr⁻¹ and respiration is 14,000 kJ m⁻² yr⁻¹, NPP is 3,500 kJ m⁻² yr⁻¹. That remainder is the energy available to higher trophic levels.

NPP is not total photosynthetic capture and is not simply plant mass. It is a rate, so the units include area or volume and time; aquatic systems commonly use volume.