[photochemsyn]

That's a standard line included in almost all photosynthesis research these days because of the global concern about fossil-fueled global warming, as a justification for continuance of one's research group funding, even if the relationship is rather minor.

The key point of this paper with respect to synthetic industrial photosynthesis:

> "Reaction-diffusion modeling of C. reinhardtii suggests that all pyrenoid-based CCMs require the following essential features: (1) aggregation of most of the chloroplast’s Rubisco enzymes, (2) a local source of high CO2 concentration at the center of this Rubisco aggregate, and (3) a diffusion barrier at the aggregate border to prevent CO2 leakage. Our data indicate that the PyShell contributes to the first two essential pyrenoid features (Figure 5A), and we wonder whether the PyShell may directly perform the third (Figure 5B)."

A big difference between oceanic diatoms and land plants is that the former's carbon source is bicarbonate, and diatoms convert bicarbonate (HCO3-) to CO2 which is utilized by Rubisco to fix CO2 onto a five carbon sugar which then splits into two 3-carbon species that are fed into carbon metabolism to generate lipids, amino acids, carbohydrates, etc. Increasing CO2 concentration around Rubisco makes the process more efficient (as this keeps out the O2, and avoids futile cycles where the O2 gets added to the target sugar). Some land plants (grasses, cacti) use alternative concentration systems not involving bicarbonate (bundle sheath and CAM).

The real takeaway for industrial-scale synthetic photosynthesis efforts is that it's always more efficient to preconcentrate CO2 into a 100% CO2 stream before feeding it into a reaction process with suitable robust catalysts in which O2 is removed and H2 is added to generate methanol or methane (somewhat analogous to ammonia synthesis) which (if you want to do real long-term storage) can be converted to materials like carbon fiber or diamond.