Primary Productivity
Introduced| English |
|---|
| primary productivity/ˈpraɪməri ˌprɒdəkˈtɪvɪti/ |
| biomass/ˌbaɪəʊˈmæs/ |
How fast an ecosystem makes food
- Every ecosystem runs on energy captured by its producers.
- Some ecosystems capture energy far faster than others.
- This rate of energy capture is called primary productivity.
- It sets the limit on how much life an ecosystem can support.
Gross primary productivity
- Primary productivity 初级生产力 is the rate producers capture and store energy.
- The total energy captured by photosynthesis is the gross primary productivity (GPP).
- Think of GPP as the whole paycheck a plant earns from sunlight.
- But the plant does not get to keep all of it.
Primary productivity measures…
Primary productivity is the rate at which producers capture energy and build biomass.
Minus respiration
- Producers must respire to power their own lives.
- Respiration burns some of the captured energy.
- So not all the captured energy is available for growth.
- What remains after respiration is what matters to the ecosystem.
From sunlight to stored energy
Step through how producers capture energy, use some for respiration, and store the rest as NPP.
How is net primary productivity (NPP) related to gross (GPP)?
NPP = GPP − respiration — the energy left over and stored as new growth.
The energy stored as new plant growth, available to consumers, is the net primary ____.
Net primary productivity is the energy actually available to feed the rest of the ecosystem.
Net primary productivity
- Net primary productivity (NPP) is what is left over: $\text{NPP} = \text{GPP} - \text{respiration}$.
- NPP is the energy stored as new plant growth — new biomass 生物量.
- It is the energy actually available to feed consumers.
- Warm, sunny, nutrient-rich ecosystems have the highest NPP.
Tropical rainforests and coral reefs have very high primary productivity.
Warm, sunny, nutrient-rich places like rainforests and reefs are the most productive.
Select all true statements about primary productivity.
NPP is less than GPP because respiration is subtracted. The other three are correct.
Do not confuse GPP and NPP. GPP is all the energy captured; NPP is what is left after the plant respires. Only NPP is available to the animals that eat the plants — so it is NPP, not GPP, that limits the ecosystem.
Comparing two ecosystems:
- A tropical rainforest is warm, wet, and sunlit — its NPP is huge.
- A desert has little water, so its producers grow slowly — low NPP.
- The rainforest can support far more animal life, because its producers store far more energy.
Primary productivity is the rate producers capture and store energy. Gross primary productivity (GPP) is all the energy captured; net primary productivity (NPP) is what remains after respiration: $\text{NPP} = \text{GPP} - \text{respiration}$. NPP is the new biomass available to consumers, and it sets how much life an ecosystem can support.