Tuesday, October 23, 2012

Pensive Tuesday: CAM Makes It Happen!

My topic of contemplation for this Tuesday is more scientific than philosophical. It amazes me that certain plants can thrive is such arid, hostile environments as the world's deserts and beachy dunes. How do they do it? How can they simultaneously deal with all that hot sunlight, and that lack of water?

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.

A Crassula

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


  1. Very interesting post! Back when I had my tillies in the solarium, they went for months without water and were just fine. Now I know that it was CAM to the rescue! They're happier now in the greenhouse where they get sprayed with water whenever the orchids are watered, but they can survive amazingly well for long periods of time without any water.

    This makes me wonder if some orchids can also use CAM, given how drought-tolerant they are. I'll have to look it up.

  2. I've seen native tillies in Florida survive looooong droughts. It's interesting you'd bring up CAM in orchids, Elly, because there is at least one NSF-funded project looking at CAM in orchids right now! I do know that about half of orchid species use CAM photosynthesis at least some of the time. I don't know which, if any, are obligates, or under what circumstances CAM photosynthesis can be triggered. A very cool area of current botanical research....

  3. That's very interesting Marla! If I was a plant, I'd definitely like to have CAM photosynthesis, because I would ideally be basking in the sun all day, under filtered sunlight of course. :)

    1. I would choose CAM, too, because I love the American Southwest and then I could just bask in the desert sun all day!

  4. Hi Marla,

    Thank you for this post. One of the rather disturbing things going on right now in regard to photosynthesis are the studies in genetic modification of cereal grasses from C3 to C4 type photosynthesis. While there are so many benefits to crop production there also are so many unknown factors that could affect the environment. Do you know what, if any, GMO studies are being done surrounding CAM?


    1. I don't know of any GMO CAM studies (doesn't mean there aren't any), but from what I know of GMO corn and soy, your news is very disturbing!