Now this is mostly aquatic type plants, I have a number of planted Aquariums.

Plants take in CO2, and exhale Oxygen during the day, ie lights on.
To some extent I can control the amount of oxy by feeding well, and lots of light. Most of my tanks operate in the 3 to 5 watts per gallon range.

They actually reverse some at night and output CO2.

This is why many aquarists, myself as one, that inject CO2 during the lighting periods, turn the CO2 injection OFF when the lights are off.
Yes, I inject CO2, the normal level in an aquarium is not nearly sufficient for plant growth.

Not exactly an answer too your question, but meant so you understand, that you can control the amount of CO2 absorbed by fertilizing and light. And that plants do exhale CO2 some, when there is no light.
I do not believe plants can survive in light 24x7.

__________________
KLK, MCSE

1990 500SL

I was always taught to respect my elders.
I don't have to respect too many people anymore.