In: Biology
NPP or Net Primary Productivity is the rate at which an ecosystem accumulates energy or biomass. This energy excludes the energy that the ecosystem has used for the process of respiration.
In a simple way it can be expressed as : the rate of photosynthesis minus respiration by the photosynthesizers.
OR
NPP = GPP - RES [ here GPP is the total rate at which an ecosystem captures and stores carbon as plant biomass for a given period of time]
Measurement of NPP varies according to the ecosystem; whether it is terrestrial or aquatic. If terrestrial, then whether it is a grassland, a forest or a desert area.
If we consider NPP on a Global scale then we have to keep in mind that NPP is an important part of the carbon cycle . Also, quantifying NPP at this scale is difficult because of the diverse habitats on the earth.
On an average, land production is estimated to be in the range of 400 to 450 g C m^-2 yr^-1 [ excluding those areas with a permanent ice cover ].
For oceans , it was estimated to be around 140 to 150 g C m^ -2 yr^-1.
Taking these values into acount, we can say that an NPP of 50 g C m^ -2 day^ -1 is on the higher side.