C3 carbon fixation
C3 carbon fixation is the most common of three
- CO2 + H2O + RuBP → (2) 3-phosphoglycerate
This reaction was first discovered by
Plants that survive solely on C3 fixation (C3 plants) tend to thrive in areas where sunlight intensity is moderate, temperatures are moderate,
C3 plants cannot grow in very hot areas at today's atmospheric CO2 level (significantly depleted during hundreds of millions of years from above 5000 ppm) because
C3 plants lose up to 97% of the water taken up through their roots by transpiration.
The isotopic signature of C3 plants shows higher degree of 13C depletion than the C4 plants, due to variation in fractionation of carbon isotopes in oxygenic photosynthesis across plant types. Specifically, C3 plants do not have PEP carboxylase like C4 plants, allowing them to only utilize ribulose-1,5-bisphosphate carboxylase (Rubisco) to fix CO2 through the Calvin cycle. The enzyme Rubisco largely discriminates against carbon isotopes, evolving to only bind to 12C isotope compared to 13C (the heavier isotope), attributing to why there's a low 13C depletion seen in C3 plants compared to C4 plants especially since the C4 pathway uses PEP carboxylase in addition to Rubisco.
Not all C3 carbon fixation pathways operate at the same efficiency.
Bamboos and the related rice have an improved C3 efficiency. This improvement might be due to its ability to recapture CO2 produced during photorespiration, a behavior termed "carbon refixation". These plants achieve refixation by growing chloroplast extensions called "stromules" around the stroma in mesophyll cells, so that any photorespired CO2 from the mitochondria has to pass through the RuBisCO-filled chloroplast.
Refixation is also performed by a wide variety of plants. The common approach involving growing a bigger
Synthetic glycolate pathway
C3 carbon fixation is prone to
Instead of optimizing specific enzymes on the PR pathway for glycolate degradation, South et al. decided to bypass PR altogether. In 2019, they transferred