CO2 supply-demand coordination in photosynthesis when Rubisco and RuBP regeneration are co-limiting: supply & demand functions from Laisk dataset

● Laisk method uses truncated A/Ci curves (demand function, DF) to estimate Ci* and Rd. In Laisk dataset, the Ca-Ci relationship reflects the supply function (SF), and points (Ci, A) for the same Ca can be fitted to a regression line (referred to Supply and Demand Function, DSF). ● The application of DSF to estimating Ci* and Rd by Laisk method and the relationship between DSF slope (dsf) and gs, and photosynthetic parameters were investigated in this study. ● Results showed that dsf was not affected by Laisk measurement conditions (PAR or Ca), while, it was inversely related to gs, apparent carboxylation efficiency (ACE) and apparent quantum yield (AQY). The dsf was essentially the slope of a light response curve (△A/△Ci-lrc) at low Ci. We devised an auxiliary line vertical to DSF and used it to improve the stability of Ci* and Rd estimates from Laisk data set for. ● We found that DSF slope was species-specific and independent of PAR and Ca. The dsf related CO2 diffusion to biochemical characteristics and represents the coordination between the two when Rubisco and RuBP regeneration co-limit photosynthesis. In conclusion, dsf can be used to describe the intrinsic characteristics of photosynthesis.