C3 carbon fixation
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Image:Calvin-cycle3.png C3 carbon fixation is a metabolic pathway for carbon fixation in photosynthesis. This process converts carbon dioxide and ribulose bisphosphate (RuBP, a 5-carbon sugar) into 3-phosphoglycerate through the following reaction:
- 6 CO2 + 6 RuBP → 12 3-phosphoglycerate
This reaction occurs in all plants as the first step of the Calvin cycle. In C4 plants, carbon dioxide is drawn out of malate and into this reaction rather than directly from the air.
Plants that survive solely on C3 fixation (C3 plants) tend to thrive in areas where sunlight intensity is moderate, temperatures are moderate, carbon dioxide concentrations are around 200 ppm or higher, and ground water is plentiful. The C3 plants, originating during Mesozoic and Paleozoic era, predate the C4 plants and still represent approximately 95% of Earth's plant biomass.
The isotopic signature of C3 plants shows higher degree of 13C depletion than the C4 plants.
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