GROSS PRIMARY PRODUCTION (GPP)
Gross primary production (GPP) is the rate at which plants capture and fix
(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 the maintenance of existing tissues.
NET PRIMARY PRODUCTION (NPP)
The remaining fixed energy is referred to as net primary production (NPP). It is
the rate at which all the plants in an ecosystem produce net useful chemical
energy, and it is equal to the difference between the rate at which the plants
produce useful chemical energy (GPP) and the rate at which they use some of
that energy during respiration.
NPP = GPP – plant respirationSome net primary production goes toward the growth and reproduction of
primary producers, while some is consumed by herbivores. Open oceans, due to
their large proportion of Earth’s surface, collectively have the highest net
primary productivity. However, when compared on a one-to-one per square
meter basis, estuaries have the highest net primary productivity.
Figure 4.3 Net Primary Productivity—compared per square meter