At night, when plants are not producing glucose (via photosynthesis), they are growing and developing (burning that glucose).
To do this they use normal "animal" metabolic pathways (i.e. Krebs Cycle), respiring CO2.
At least I think that's right....
Some plants have unique metabolic pathways too (CAM, C-4 plants).
I'd think 100% CO2 would kill a plant within a day.
I think even 4-5% will kill a plant. I know there is some fairly low optimum, over which higher concentrations are detrimental.
How much C02, or even how little Oxygen would be required by a plant to grow and live would make an interesting project
I know the Americans built a closed greenhouse with all sorts of plants in it. Putting in a couple of scientists, to see just how long they might survive, about 30 years ago.
Then again, 60 million years ago, and even before the Dinosaurs ruled the Earth.
Plant and tree life was huge, when we had less Oxygen in the atmosphere than today.
Interesting huh?
