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.

Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.