I know that a greenhouse is not air tight so I imagine it breathes somewhat and exchanges gas with the outside. However, I also assume that it’s going to use up the co2 in it for plant growth. How does it not run out? I think you could vent it, but then wouldn’t that cool it off and thus defeat the purpose of a greenhouse? All my web searches either give climate change facts or co2 supplementation by farmers.
To add; I’d imagine decomposition of compost further contributes to CO2. The fact that CO2 is pumped in to some commercial greenhouses suggests CO2 is a limiting factor in plant growth, but I wonder whether hydroponic systems - lacking soil and hence decomposition - require more.