Reduced mesophyll conductance induces photosynthetic acclimation of japonica rice under elevated CO2

Abstract The foliar photosynthetic acclimation to prolonged elevated CO2 has been studied in many ways, but the quantification of photosynthetic acclimation through the limitation of stomatal conductance (gs), mesophyll conductance (gm) and biochemical capacity (Vcamx) is scarce. To quantify photosynthetic acclimation under elevated CO2, a japonica rice cultivar ‘Nanjing 9108’ was grown at two CO2 levels—ambient CO2 (a[CO2]) and a[CO2] +200 μmol mol−1 (e[CO2]) using open top chamber facility. We measured the response of net photosynthetic rate (An) to CO2 at Rubisco (Cc) at jointing, flowering and filling stages based a biochemical C3‐photosynthesis model. Measurements at the same CO2 concentration showed that the An under e[CO2] was significantly lower than that under a[CO2] at three developmental stages, suggesting the occurrence of acclimation of photosynthesis. The photosynthetic acclimation is associated with the decrease in gm, gs and Vcmax, and gm mainly limits photosynthesis. The contribution of gm, gs and Vcamx limitation to photosynthetic acclimation averaged 65 %, 25 % and 10 % of the total reduction in An. Our findings demonstrate gm is the major driver of photosynthetic acclimation and highlight the role of gm under e[CO2] in rice.