Boosting the percentage of CO2 in the air of your grow room can boost plant growth rate and increase plant leaf output. In a grow room, boosting the CO2 level is a way to create an envelope of CO2. Plants draw in or "breathe" CO2 from the stomas in the undersides of their leaves. They exhale oxygen. By boosting the CO2 within the envelope, your plants will not only breathe more deeply, they will draw up more water and be able to store more nutrients in their flesh. Finally, boosting daytime CO2 exposure can increase the flowering output of your plants.