GPP and NPP
Photosynthesis is very inefficient. Green plants only capture a small amount of the solar energy that actually reaches them, and turn it into gross primary production (GPP). GPP is the total energy fixed by photoautotrophs during photosynthesis.
Some sunlight passes straight through a leaf, and some is reflected from the surface of the leaves. Certain parts of the visible spectrum cannot be utilised by the plant for photosynthesis.
GPP: the rate at which solar energy is captured in sugar molecules during photosynthesis (energy captured per unit area per unit time) – the total energy accumulated by plants before any losses to photosynthesis.
Net Primary Productivity (NPP) is the energy captured by plants through photosynthesis that remains after subtracting the energy they use for respiration from GPP.
It represents the amount of biomass available to herbivores and higher trophic levels in an ecosystem.
NPP varies depending on factors such as sunlight, temperature, water availability, and nutrient levels.
Only a fraction of the energy plants capture becomes NPP, making it a key measure of an ecosystem’s energy available for consumption and growth.
High NPP areas, like tropical rainforests and coral reefs, support greater biodiversity, while low NPP areas, such as deserts, sustain fewer organisms.
NPP: the rate at which energy is stored as biomass by plants or other primary producers and made available to the consumers in the ecosystem.
NPP = GPP – Energy lost in respiration
Secondary Production
Energy flow through consumer populations considers what happens to the energy they consume from food. Much of this energy is used for respiration, movement and maintaining body temperature, and some is lost as waste.
The energy that is incorporated into new consumer tissue is called secondary production.
When the energy used in respiration is subtracted, the result is net secondary production – the energy available to the next trophic level.
Net secondary production depends on factors such as the efficiency of digestion, metabolism and growth rates, and it is generally much smaller than the energy originally captured by primary producers.
N = I – (F + R)
N = Secondary production
I = Chemical energy ingested
F = Energy lost through faeces and urine R = Energy respiratory losses to the environment