It turns out there are 3 forms of photosynthesis, and the type called CAM is the answer I was seeking. CAM stands for Crassulacean Acid Metabolism, because it was first discovered in the family Crassula (one of the succulent collector's favorites) in the 1890s.
CAM can be used exclusively by a plant, or just when things get hot and dry. Most of the plants in this blog, mesembs, Tillandsias, cacti, are CAM obligates- it's the only type of photosynthesis they have. What makes CAM so special?
Basically, CAM saves water. Most plants lose about 97% of their water each day to evapotranspiration. CAM allows plants to keep their stomata (pores) closed during the hot, dry day, and to open them at night when evaporation is at a minimum. CAM is a two-part process whereby the plant allows carbon dioxide in at night, fixes it into organic acids, stores those in vacuoles. During the day, it sends the malate to the chloroplasts, so the plant can photosynthesize with its stomata closed. It requires a lot more solar energy, but a lot less water. These plants get lots of sun, but not much water, so it works. CAM also allows a plant to essentially go dormant for longish periods during droughts, and then "wake up" when the rains or mists return. It's called a "CAM Idle", and many mesembs and cacti can do this. So can some Tillies. Ordinary plants just die during long droughts.
So that's how they do it. Remarkable!
|CAM Expert Mammillaria nana duwei|