2.2.25 (HL)—NPP and food chains

Net primary productivity is the energy stored by producers after their own respiration: NPP = GPP − R.

Gross primary productivity counts all fixation. Producers use some fixed energy to maintain cells; the remainder becomes biomass available to consumers and decomposers.

If GPP is 500 and plant respiration is 180 g C m⁻² y⁻¹, NPP is 320 g C m⁻² y⁻¹.

It falls to 260; more fixed carbon is spent by producers before it can enter the food web.

NPP is not GPP plus respiration; respiration is the deduction from gross fixation.