CAM and C4 Metabolism?

[Arizona Jeanie]

OK, I don't have a strong background in chemistry or botany , but maybe ya'll could help me understand this a little better. I have noticed some references on orchid board to CAM and C4 metabolism in orchids. It's challenging, I know, but can anyone simplify this to where I might be able to understand it? Basic bottom line question is how it changes the care of orchids vs other "typical" plants, and why?
Thanks!

[naoki]

You can think that C3 plants open stomata during the day, and CAM plants open them during the night.

Stomata need to open for gas exchange. If the O2 concentration becomes too high (as a by-product of photosynthesis), the plants start to lose carbon instead of assimilating. But as a side effect, water gets lost (undesirable for plants). So you want to keep the air humidity high during the day for C3 and during the night for CAM in principle.

CAM plants use C4 pathway. You can think it as a method to increase water use efficiency. So far, orchids are eitther C3 or CAM, and I don't think C4 orchids have been discovered. Even CAM orchids are frequently facultative, so when there is enough water, they behave like a C3 plants (Phalaenopsis is an example of facultative CAM).

[estación seca]

CAM plants (Crassulacean Acid Metabolism) generally don't tolerate hot nights. Their respiration (oxygen and carbon dioxide exchange) doesn't function at higher temperatures. How hot varies from species to species.

Succulents in the Crassula family (for which CAM was named) often collapse into mush after 2-3 nights over 85 F / 30C. This includes many Crassula, Aeonium, Echeveria and Sedum. Same goes for many succulent bromeliads, especially Tillandsia, and many higher-elevation cacti and aloes.

Some succulents are just fine with hot nights, while close relatives in the same family are not. I don't know whether their enzyme systems have been studied in enough detail to figure out their adaptations. But many Brazilian and Baja California succulents flourish with very high night temperatures.

We orchid growers know many orchids prefer cooler night temperatures to grow well, and suffer with steady high temperatures. This is a large part of the reason.

[Arizona Jeanie]

Thank you, that helps! So maybe the cooler mountain nights here (for most of the year) aren't a bad thing for the phals. I was a little surprised when I discovered they could do pretty well in my dark and non-climate controlled home. A lot of my other plants have faded away here, I'm sure enjoying the orchids!

[dangerouseddy]

here's a technical pdf on the CAM mechanism :-

Crassulacean Acid Metabolism in Epiphytic Orchids: Current Knowledge, Future Perspectives | InTechOpen