CO2 speeds growth. The more you add, the more they absorb and the quicker they grow. CO2 isn't utilized by the plants in any other way, other than growth. As I understand it, it is possible (in theory anyway, not sure how this pans to practice) to grow most plants in a low-CO2 environment provided they have everything else they need.
Light and CO2 need to be in balance otherwise you'll end up with hungry plants and discoloured leaves etc.
Plants will react differently in nature and share similarities with their parent plant (like, for example, I have my Mother's eyes). If the parent plant has adapted to a certain CO2 level, whether that be higher or lower than what's in the aquarium then chances are the offspring plant will be more suited to a lower or higher CO2 environment.
Plants that are brought up in the aquarium will be used to utilizing a certain amount of CO2 and will definitely die or at the very least melt and stay melted for a while, if you were to stick it in it's natural habitat.
Hope this sort've makes sense.
A lot of people forget that plants, although they don't have eyes and mouths, are still living things and therefore evolution and genetics still apply.