When do desert plants take up carbon dioxide and perform photosynthesis?

Desert plants take up carbon dioxide and perform photosynthesis mainly at night.

These plants, which are typically adapted to arid environments, use a specialized type of photosynthesis known as Crassulacean Acid Metabolism (CAM). Unlike most plants that open their stomata during the day to take in carbon dioxide for photosynthesis, desert plants open their stomata at night. This adaptation helps them reduce water loss because the cooler night temperatures minimize the evaporation of water, which is critical for survival in the hot, dry desert climate.

Here's how CAM photosynthesis works:

Nighttime: During the night, desert plants open their stomata and absorb carbon dioxide from the atmosphere. This carbon dioxide is then converted into organic acids, mainly malic acid, and stored in vacuoles.
Daytime: During the day, the stomata remain closed to prevent water loss. The stored malic acid is broken down to release carbon dioxide inside the plant cells. This CO2 is then used in the Calvin cycle for photosynthesis to produce glucose.
This unique mechanism allows desert plants to conserve water while still being able to carry out photosynthesis efficiently.