GPP and NPP
Gross primary production (GPP) is the rate at which an ecosystem's producers capture and store a given amount of chemical energy as biomass in a given length of time. Some fraction of this fixed energy is used by primary producers for cellular respiration and maintenance of existing tissues (i.e., "growth respiration" and "maintenance respiration"). The remaining fixed energy (i.e., mass of photosynthate) is referred to as net primary production (NPP).
- NPP = GPP - respiration
Net primary production is the rate at which all the plants in an ecosystem produce net useful chemical energy; it is equal to the difference between the rate at which the plants in an ecosystem produce useful chemical energy (GPP) and the rate at which they use some of that energy during respiration. Some net primary production goes toward growth and reproduction of primary producers, while some is consumed by herbivores.
Both gross and net primary production are in units of mass / area / time. In terrestrial ecosystems, mass of carbon per unit area per year (g C/m2/yr) is most often used as the unit of measurement.
Read more about this topic: Primary Production