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

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 (g(s)), mesophyll conductance (g(m)) and biochemical capacity (V-camx) 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 mu mol mol(-1) (e[CO2]) using open top chamber facility. We measured the response of net photosynthetic rate (A(n)) to CO2 at Rubisco (C-c) at jointing, flowering and filling stages based a biochemical C3-photosynthesis model. Measurements at the same CO2 concentration showed that the A(n), 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 g(m), g(s) and V-cmax, and g(m) mainly limits photosynthesis. The contribution of g(m), g(s) and V-camx limitation to photosynthetic acclimation averaged 65 %, 25 % and 10 % of the total reduction in A(n). Our findings demonstrate g(m) is the major driver of photosynthetic acclimation and highlight the role of g(m) under e[CO2] in rice.

Automated summary

The study investigated the photosynthetic acclimation of a japonica rice cultivar under elevated CO2 levels, finding that the decrease in photosynthetic rate was mainly limited by mesophyll conductance (g(m)). The results underscore the significant role of g(m) in photosynthetic acclimation under elevated CO2 conditions in rice.