How can the lack of water in an environment affect the amount of carbon dioxide absorbed by the plant?

Les carbon dioxide would be taken in and the stoma would close more often to hold on to the water the plant has. Water is split to replace electrons lost from chlorophyll excitation by photons, so, not having a sufficient supply of water would greatly slow the photosynthetic process. Not to mention the turgidity problems lack of water would exacerbate.

So, with the stoma closed more often less CO2 would diffuse into the leaf.