Desert plants take in carbon dioxide (CO2) at night primarily to minimize water loss during the hot desert days.
The Challenge of Desert Life: Water Conservation
In arid environments, water is scarce. Plants face a constant struggle to survive without losing too much water through transpiration, the process where water evaporates from the leaves.
The CAM Solution: A Two-Step Process
Many desert plants, called Crassulacean Acid Metabolism (CAM) plants, have evolved a unique adaptation to deal with this problem. CAM allows plants to separate the processes of CO2 uptake and carbon fixation into night and day, respectively.
Nighttime CO2 Uptake: Keeping Stomata Closed During the Day
- Stomata: These are tiny pores on the surface of plant leaves (and sometimes stems) that allow for gas exchange. Plants need to open stomata to take in CO2 for photosynthesis, but opening them also leads to water loss.
- Why Night? During the cooler nighttime hours, the rate of evaporation is significantly lower than during the day. CAM plants open their stomata at night, allowing them to take in CO2 with minimal water loss.
- Malic Acid Storage: The CO2 that is taken in is then converted into an organic acid, typically malic acid, and stored in vacuoles within the plant cells.
Daytime Carbon Fixation: Photosynthesis with Stomata Closed
- Stomata Closure: During the day, when temperatures are high and water loss is a significant risk, CAM plants keep their stomata closed.
- Using Stored CO2: The malic acid stored from the previous night is broken down, releasing CO2 inside the plant cells.
- Photosynthesis: This CO2 is then used in the Calvin cycle to produce sugars through photosynthesis, even though the stomata are closed, preventing water loss.
Advantages of CAM
- Water Conservation: CAM significantly reduces water loss compared to plants that keep their stomata open during the day.
- Survival in Arid Environments: This adaptation allows CAM plants to thrive in deserts and other dry environments where water is limited.
Examples of CAM Plants
Many succulents, cacti, and other desert plants utilize CAM, including:
- Cacti
- Agave
- Succulents like Sedum and Kalanchoe
- Pineapple
In summary, desert plants that utilize CAM photosynthesis take in CO2 at night to minimize water loss, a crucial adaptation for survival in arid environments where water is a scarce resource.
