Net primary productivity is the net difference between photosynthesis and respiration in an ecosystem.
In other words, it’s how much carbon dioxide plants take in during photosynthesis minus how much they release during respiration.
Think of it like a savings account:
It’s how much carbon that trees fix. Then, you subtract the amount of carbon that trees respire. This gives you the net primary productivity.
Net primary productivity can only be negative if a plant’s cellular respiration rate is lower than it’s photosynthetic rate.
The most productive ecosystems
Lush tropical rainforests are the most productive places on the planet.
Throughout the whole year, rainforests in South America, Africa and Southeast Asia have high net primary productivity.
Whereas countries in the mid-latitudes have seasonal variations.
For example, spring and summers exhibit high net primary productivity in North America, Europe and Russia.
But as winter comes, the rate at which plants absorb carbon dioxide out of the atmosphere dampens.
The least productive ecosystems
Polar regions and deserts are the least productive because both types of ecosystems experience little photosynthesis year-round.
Not only are tundras cold in temperature, but they receive little for rainfall. This is why high-latitude ecosystems have sparse vegetation so there is minimal energy flow.
While Antarctica is a cold desert, hot deserts are covered in sand with little rainfall. They have hostile living conditions for plants and animals so net primary productivity is quite low.