Light Intensity Dependence of CO₂ Assimilation Is More Related to Biochemical Capacity Rather than Diffusional Conductance

Abstract

The response of CO2 assimilation rate (AN) to incident light intensity reflects the efficiency of light utilization. The light intensity dependence of AN varies widely among different plant species, yet the underlying mechanisms remain poorly understood. To elucidate this issue, we measured the light intensity dependence of gas exchange and chlorophyll fluorescence in twelve tree species. The results indicated that (1) with increasing light intensity, the variation in AN was closely related to stomatal conductance (gs), mesophyll conductance (gm), the maximum velocity of Rubisco carboxylation (Vcmax), and electron transport rate (ETR); (2) compared with AN at sub-saturating light, the increase in AN at saturating light was more strongly associated with Vcmax and ETR than with gs and gm; and (3) the increase in Vcmax and AN from 600 to 2000 μmol photons m−2 s−1 were positively correlated with the maximum capacity of Vcmax. These findings suggest that Vcmax is an energy-dependent process that significantly regulates the light intensity dependence of AN in plants. This provides valuable insights for crop improvement through the manipulation of Vcmax.

Keywords

• photosynthesis
• light response
• Rubisco carboxylation
• stomatal conductance
• mesophyll conductance