Are you ever right.  Many comercial greenhouses increase CO2 levels from 240PPM or .024% all the way to 700PPM or .07% and can double vegetable production with high quality products.  Plants produce 3 times more glucose which ends up giving plants more vigor and healthy growth.  And yes, the CO2 concentration is constantly monitored to regulate CO2 levels.  What is very interesting is that when the roof vents in the greenhouses open for cooling purposes during the day, the CO2 levels drop well below 300PPM or .03% which was the official number for atmospheric CO2 when I was in college many years ago.  Bottom line is that FAKE science is telling us the big lie that CO2 levels are rising globally when they actually are not, they vary within 240 or  to 300PPM, .024% to .03% respectively.