20 – 40 mM
||Wang Y, Stessman DJ, Spalding MH. The CO2 concentrating mechanism and photosynthetic carbon assimilation in limiting CO2 : how Chlamydomonas works against the gradient. Plant J. 2015 May82(3):429-48. doi: 10.1111/tpj.12829 p.444 left column bottom paragraphPubMed ID25765072
||Price GD, Badger MR, Woodger FJ, Long BM. Advances in understanding the cyanobacterial CO2-concentrating-mechanism (CCM): functional components, Ci transporters, diversity, genetic regulation and prospects for engineering into plants. J Exp Bot. 2008 59(7):1441-61 DOI: 10.1093/jxb/erm112PubMed ID17578868
||P.444 left column bottom paragraph: "The eukaryotic algal CCM may have unique advantages for transferring a CCM to higher plants, because eukaryotic algae and vascular plants share close evolutionary relationships and similar photosynthetic and many other molecular characteristics. The typical 2–3 mM stromal HCO3– concentration apparently required for microalgal CCM function (BNID 114619) may also be much easier to achieve than the 20–40 mM internal HCO3– concentration characteristic of the typical cyanobacterial system (primary source)."