Plants that live in extremely hot and arid climates often keep their stomata closed during the day, to reduce the amount of water that is lost in transpiration, and open it during the cooler and more humid nighttime. This system is called Crassulacean acid metabolism (CAM), or CAM photosynthesis, and the plants that use it are referred to as CAM plants. These plants fix CO₂ at night, avoiding water loss by not opening their stomata during the day, and release the CO₂ during the day. CAM plants include succulents, cacti, bromeliads, orchids, and others.

In contrast to CAM photosynthesis, most plants on Earth (making up 95% of the Earth's plant biomass) undergo C₃ carbon fixation, living in areas with moderate sunlight, moderate temperature, and plenty of ground water. They lose approximately 97% of the water taken up by their roots to transpiration -- the cost of having stomata open during the day, something the arid-dwelling CAM plants cannot afford to do.

Hi, thanks for the question! As you may know, plants have pores or openings on their leaves and stems called stomata. This name comes from Greek for "mouth". These pores allow carbon dioxide to enter the leaves and oxygen water to escape. Plants can respond to light and heat and humidity and even the wind by altering how open the pores are. The pore size is regulated by specialized cells called "guard cells" which become more of less swollen as the conditions require.In hot, dry areas, such as the desert, plants have evolved ways to avoid losing a lot of water during the day. They perform "Crassulacean Acid Metabolism" or CAM, photosynthesis. In these plants, the stomata are closed during the day and open during night to allow for CO₂ and water transfer. Hope this answers your question!