CO2 supplementation is a common and highly beneficial practice in modern horticulture. This document will explain why, when, and how supplementation is important and what the potential outcomes can be.
Different types of plants, different biological processes
Plants are characterized by how they acquire CO2 and what type of carbohydrates they create during photosynthesis. Plants’ photosynthesis pathways are divided into 3 categories: C3, C4, and CAM. C3 accounts for 95% of the species on earth, the rest are equally divided between C4 and CAM.
- C3 :
- Classified as such because they produce a compound with 3 carbon atoms as a product of photosynthesis.
- This type of plant wants CO2: it boosts the production of carbohydrates available for growth by opening the stomata.
- C4:
- Photosynthesis produces a compound/molecule with 4 carbon atoms.
- Includes mostly grass-like plants like corn and cereal grains.
- CO2 is stored indirectly in internal holding sites.
- Stomata open only when they need to restore CO2. This particular timing makes the CO2 supplementation almost useless.
- CAM:
- Stands for Crassulacean Acid Metabolism.
- Fixation of the carbon evolved to adapt to arid conditions.
- Open their stomata at night to collect CO2 instead of during the day.
- Typically Cactus and succulents.
Photosynthesis Reaction: The Importance of CO2
Photosynthesis is divided into two sub-processes: a light dependent reaction and a light independent reaction. The light independent reaction, also known as the Calvin cycle, doesn’t need light to occur, as it occurs during the day and night.
- Light Dependent reaction: H2O + light -> ATP + NADPH + O2
- Light independent reaction: ATP + NADPH + CO2 -> Carbohydrates
Combining those two give an overall reaction as follows:
H2O + CO2 + Light -> Carbohydrates + O2
Or
Water + Carbon dioxide + light -> Carbohydrates + oxygen
Carbon dioxide is therefore vital and necessary for plants to thrive, whether they are C3, C4 or CAM. The difference between the categories is how they assimilate the carbon dioxide to be used as a source of energy and build carbohydrates.