At night, when plants turn off their photosynthesis and undergo respiration (the intake of oxygen and release of carbon dioxide), carbon is replaced back into the air.
(plants; undergo; respiration) (carbon; is replaced; back into the air; T:At night; T:when plants turn off their photosynthesis and undergo respiration)
plants carbon
undergo is replaced
respiration
back into the air T:At night T:when plants turn off their photosynthesis and undergo respiration