Carbon Capturing Mechanisms in Opuntia

Opuntia, a prickly pear cactus, employs a unique photosynthetic pathway called Crassulacean Acid Metabolism (CAM) to capture and store carbon dioxide (CO₂). The CAM pathway allows Opuntia to optimize its carbon-capturing efficiency while minimizing water loss, making it well-adapted to arid and semi-arid environments. The carbon-capturing mechanisms in Opuntia can be explained through the following steps:

1. CO₂ uptake during the night

Unlike most plants that take in CO₂ during the day, Opuntia opens its stomata (tiny pores on leaves or cladodes) at night. This nocturnal behavior helps the plant to capture CO₂ when the temperature is more relaxed, and the humidity is higher, reducing water loss through transpiration.

2. Storage of CO₂ as malic acid

Once CO₂ enters the plant through the stomata, it is combined with phosphoenolpyruvate (PEP) to form oxaloacetate, which is then converted to malic acid. Malic acid is stored in the plant’s vacuoles as a temporary reservoir for the captured CO₂.

3. Release of CO₂ during the day

During the daytime, when the stomata are closed, the stored malic acid is transported to decarboxylated chloroplasts, releasing CO₂. The plant’s photosynthetic machinery uses this CO₂ to produce glucose and other organic compounds through the Calvin cycle.

4. Carbon storage in plant biomass

The plant uses the glucose and other organic compounds produced during photosynthesis for growth and maintenance. As the plant grows, more carbon is stored in its biomass, sequestering the captured carbon from the atmosphere.

In summary, Opuntia’s CAM pathway allows it to efficiently capture and store carbon by taking CO₂ at night and utilizing it for photosynthesis during the day. This unique adaptation enhances the plant’s carbon-capturing potential and helps it conserve water in arid and semi-arid environments.

https://link.springer.com/article/10.1007/s13593-017-0481-3