Metabolism slows down. CAM plants in general grow slowly and have a low metabolic rate, and under prolonged dry conditions they can reduce metabolism further and reuse some of the CO2 generated by respiration.

What exactly does C A M stand for?

Crassulacean Acid Metabolism. It allows certain plants to fix CO2 at night (as malic acid) and use it during the day for photosynthesis while keeping their stomata closed, allowing them to survive in environments with limited water availability. It is common in epiphytic and desert plants. The term "crassulacean" is just a reference to the family of plants where this pathway was first found.