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The secret of CAM photosynthesis: How does this adaptation help plants survive drought?
How do plants survive and photosynthesize efficiently in hot, dry environments? This is a problem that constantly challenges plant survival. Today, we will explore a special photosynthesis method called Crassulacean acid metabolism (CAM) and how it helps plants thrive in extreme climates.
CAM photosynthesis is a carbon fixation pathway that some plants have evolved to adapt to drought conditions.
CAM photosynthesis enables plants to photosynthesize during the day and perform gas exchange only at night. In this special photosynthesis mechanism, the stomata of plants remain closed during the day to reduce evapotranspiration; while at night, the stomata open to absorb carbon dioxide (CO2) from the atmosphere. These CO2 are stored as four-carbon malic acid, which is converted into CO2 during the day and then participates in photosynthesis. This process not only improves the efficiency of photosynthesis, but is also critical to plant survival in arid environments.
Historical background
Early observations of CAM photosynthesis date back to 1804, when scientists explored it as part of plant physiology. Over time, many scholars have conducted in-depth research on it and established the basic concept of CAM. Therefore, this relatively high-risk evolutionary mechanism first appeared in the succulent plant family (Crassulaceae), especially plants such as Gyokuro.
Although the name of CAM metabolism is derived from Crassulaceae, it does not actually involve any specific "Crassulacean acid".
CAM operating mechanism
CAM photosynthesis has two main processes: nocturnal and diurnal variations.
Night process
At night, plant stomata open and CO2 can enter. During this process, CO2 reacts with phosphoenol (PEP) to form organic acids, which are stored in cellular vacuoles. This is because the Calvin cycle cannot operate at night because it relies on ATP and NADPH produced by light reactions.
Daytime process
During the day, the stomata close to protect moisture and stored organic acids are released. Then, the CO2 in these organic acids enters the Calvin cycle in the chloroplasts to complete the process of photosynthesis.
For CAM plants, the most important benefit is that most stomata can be closed during the day. This makes it possible for them to survive in dry environments.
Comparison with C4 metabolism
There are similarities between CAM and C4 photosynthesis, both can improve the efficiency of CO2 utilization. CAM provides the CO2 needed during the day through concentration in time, while C4 concentrates in space. This means they use different but equally effective strategies to adapt to dry conditions.
Survival strategies of CAM plants
In nature, some plants are called "strong CAM plants" or "weak CAM plants" depending on the amount of organic acids they can store. Other plants can switch from C3 or C4 to CAM according to changes in environmental conditions. The survival ability of these plants changes with the alternation of drought and non-drought, demonstrating their extremely high adaptability.
Existence of aquatic CAM
CAM photosynthesis occurs not only in terrestrial plants, but also in aquatic plants, and they also need to cope with the lack of CO2 in similar ways. The diffusion rate of CO2 in water is much slower than in air, making this mechanism necessary to maintain photosynthesis efficiency.
Ecology and taxonomic distribution
Most plants with CAM properties are epiphytes (such as orchids) or fleshy, arid plants (such as cacti). However, some trees, such as some species in the genus Clusia, also exhibit characteristics of CAM, demonstrating their diversity and pervasiveness in different ecological environments.
CAM, through its unique biochemical pathways, demonstrates the wisdom of plants in adapting and evolving in the face of various environmental challenges.
Conclusion
As the effects of global climate change become more apparent, how plants change their photosynthetic methods to survive has become a question worth pondering. The mystery of CAM photosynthesis not only demonstrates the survival wisdom of plants in extreme environments, but also reminds us that future ecological research needs to pay more attention to the adaptability and evolution process of plants in environmental changes. What will happen to such adaptations? Affect the development of the overall ecosystem?
