I remember from intro bio that there is a category of plants (ones using the CAM metabolism pathway) that close their stomata (openings in the leaves) during the day to save water. So all the oxygen release and CO2 intake occurs at night, and photosynthesis still occurs during the day.

I'm guessing that the plants noted in this article are in that or a similar category; Wikipedia/Googling would provide a lot more info. Cheers!