To paraphrase a famous saying without CAM there is no mezcal. CAM stands for crassulacean acid metabolism which is the way that agaves breath and hence, how they live. Without that process we wouldn’t have them or mezcal. Simple right?
I’m not a scientist so I’ll lean on the work of experts and just sketch the process. It’s absolutely fascinating and a real window into the complexity inherent in our world. Agaves grow in some very inhospitable locations that are typically arid, receive rain for a brief moment annually, and see lots of sun. Visually it’s clear that they’re set up to be survivors in inhospitable environments, they have spikes on their pencas, they’re tough, and they don’t look appetizing despite their delectability. But that tough exterior only hints at the actual process that keeps these amazing plants alive.
The basics of CAM are that agaves, and other plants that use it, only respire during the night in order to minimize the loss of any moisture. During the day their pores remain sealed shut then when the temperature drops with sundown, they open up to suck in C02 which they use for photosynthesis. This lets them survive arid environments and the lack of precipitation, yet another reason that they’re true survivors.