The answer is PRODUCERS.
Plants are producers and perform photosynthesis.
They use the sunlight, that provides them with energy, and take the carbon dioxide from the atmosphere, that helps reducing it.
Photosynthesis is a way for them to make their own food (sugars), necessary for them to stay alive and to produce oxygen. Both will be needed for their cellular respiration, a process that occurs in the mitochondria, and will produce energy, in the form of ATP, and CO2.
The carbon dioxide that they produced in cellular respiration can be used for photosynthesis.
