How does gross primary productivity differ from net primary productivity?
Gross primary production is the amount producers create over a set period of time whereas net primary productivity is former once respiration has been accounted for.
Gross primary production (GPP) is the rate at which primary producers convert energy to chemical biomass.
If you subtract the amount of energy the primary producer uses for respiration, you have the net primary production (NPP).
Much of the energy from GPP is used by the producer for cellular respiration. What energy is leftover, the NPP, is potentially available for other organisms to consume.