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.
Plants only absorb CO² and release oxygen when photosynthesizing, which requires sunlight. At night plants undergo cellular respiration where they absorb oxygen and release CO². Some sealed terrariums haven’t had any water, air, or fertilizer for decades.
https://laidbackgardener.blog/2019/10/14/the-worlds-second-oldest-sealed-terrarium/