Mesophyll conductance exerts a significant limitation on photosynthesis during light induction

Past studies have established mesophyll diffusion conductance to CO2 (gm ) as a variable and significant limitation to plant photosynthesis under steady-state conditions. However, the role of gm in influencing photosynthesis (A) during the transient period of light induction is largely unknown. We combined gas exchange with laser-enabled carbon isotope discrimination measurements to assess gm during photosynthetic induction, using Arabidopsis as the measurement species. Our measurements revealed three key findings: 1) we found that the rate at which gm approached steady state during induction was not necessarily faster than the induction rate of the carboxylation process, contradictory to what was suggested in previous studies; 2) gm displayed a strong and consistent coordination with A under both induction and steady-state settings, hinting that the mechanism driving gm -A coupling does not require physiological stability as a prerequisite; 3) photosynthetic limitation analysis of our data reveals that when integrated over the entire induction period, the relative limitation of A as imposed by gm can be as high as >35%. The present study provides the first demonstration for the important role of gm in limiting CO2 assimilation during photosynthetic induction, thereby pointing to a need for more research attention to gm in future induction studies.