They do and they don't. The net result of a growing plant is the absorption of CO2 and H2O to create O2 and various hydrocarbons, oxygen and plant matter. The carbon is fixed in the body of the plant. But i did mention grow lamps. Keep them lit and there is no night.
Plants still need to use the glucose, though. It's misleading to say that plants produce CO2 at night (since they produce it all the time); rather, they become a net CO2 producer at night because they're not offsetting it with photosynthesis.
I'm not convinced that grow lamps are an effective way to offset that, since photosynthetic efficiency is fairly low (3-4%), and the electricity for the lamp has to come from somewhere. Not to mention that lamps (even LEDs) are also fairly lossy. I'm also not convinced that's even worth optimizing.
