The carbon cycle in other words concerning plants is called the photosynthesis is a cycle in which plants feed them selfs from the atmosphere and soil nutrients,CO2(g) ,H2O in any form and sunlight (solar energy) .As you may have learned CO2 contains carbon which in a way helps the plants growth and feeds them. You can know because plants release O2 and C6H12O6(s) at the end of the cycle.