Hydroponic growers are intimately aware of the need and benefits accruing from elevated CO2. You'd be hard pressed to find a greenhouse vegetable farm without a huge CO2 tank outside, as well as the technology used inside the scrub carbon dioxide from natural gas exhaust and reroute it into the plants. They tend to burn the natural gas during the day to feed the plants while storing the heat in huge water tanks to warm facilities at night.

The primary constraint is maintaining low enough CO2 levels to remain healthy for the humans that work inside the greenhouse. Plants themselves can handle very high levels of carbon dioxide.