↵ Crassulacean acid metabolism plants (CAM plants): This dark CO2 fixation pathway proposed by Ting (1971). It occurs in succulent or fleshy plants like Cactus, Sedum, Opuntia, orchid, pineapple and Bryophyllum helping them to continue photosynthesis under extremely dry conditions.
The stomata of succulent plants remain closed during the day and open during the night to avoid water loss (Scotactive stomata). They store CO2 during the night in the form of malic acid in the presence of enzyme PEP carboxylase. The CO2 stored during the night in the form of malic acid is undergoing decarboxylation at daytime to release CO2 inside. This CO2 is used in the Calvin cycle during day time. Succulents refix CO2 released during respiration and use it during photosynthesis.
This diurnal change in acidity in the plant body was first discovered in crassulacean plants, e.g. Bryophyllum. So it is called as crassulacean acid metabolism.