Earth Observatory: Plants breathe. They take carbon dioxide from the atmosphere and turn it into the sugars that become leaves, stems, roots, and woody trunks. What carbon dioxide they don't use, they exhale, releasing the leftover gas with oxygen. And after plants die, they decay, releasing the carbon to the atmosphere. The difference between the amount of carbon plants absorb and what they release is called net primary productivity. It is a direct measurement of how much plant matter -- from crops to forests or ocean phytoplankton -- Earth produces.
