Thank you for that link, I read it. The article talks about CO2 that the plant has absorbed and then, to some degree, released. That is completely whithin the way I understand a plant works.
Much the same way that we inhale air (containing about 18% Oxygen). If we are exercising, we "burn" somewhat more oxygen; if we are at rest, we "burn" somewhat less. But either way, we don't "burn" it all. We exhale some of it back into the atmosphere. But we don't produce the Oxygen, we just release the excess.
The article doesn't say that plants PRODUCE CO2, it just says that they RELEASE what they don't use. I said I doubted that plants produce CO2 - I still do! It makes sense that a plant would release a higher concentration of CO2 at night while photosynthesis is dormant. I'll have to go back and reread that article to see if it states anything about the PPM of CO2 that one can expect - it may be significant; maybe not.
Interesting!