Photosynthetic capacity is limited by carboxylation capacity and electron transport capacity. For example, in high carbon dioxide concentrations or in low light, the plant is not able to regenerate ribulose-1,5-bisphosphate fast enough (also known RUBP, the acceptor molecule in photosynthetic carbon reduction). So in this case, photosynthetic capacity is limited by electron transport of the light reaction, which generates the NADPH and ATP required for the PCR (Calvin) Cycle, and regeneration of RUBP. On the other hand, in low carbon dioxide concentrations, the capacity of the plant to perform carboxylation (adding carbon dioxide to Rubisco) is limited by the amount of available carbon dioxide, with plenty of Rubisco left over.¹ Light response, or photosynthesis-irradiance, curves display these relationships.
