CAM (Crassulacean Acid Metabolism) / Diurnal Acid Cycle -

At night
Stomata are open. PEP Carboxylase helps in Carbon dioxide fixation. This carbon dioxide which is getting fixed has two sources - (1) starch breakdown and (2) atmosphere. In the vacuoles, malic acid gets stored.
During day
Stomata are closed. Stored malic acid breaks into pyruvate and carbon dioxide. Carbon dioxide enters C3 (Calvin) Cycle and pyruvate is utilised to regenerate PEP.
Hence at night, organic acids (malic acid) are synthesized from carbon dioxide while during day plenty of carbohydrates get produced.

• CAM cycle operates in mesophyll cells.
• CAM plants are less efficient as compared to C4 plants.
• CAM plants are better adapted to extreme dry conditions.
• CAM plants have the slowest photosynthetic rates.

Example of CAM plants - Pineapple, Opuntia