Diffuse light weakens the dorsoventral asymmetry of photosynthesis in sorghum leaves

Dorsoventral asymmetry of photosynthesis is important for light use patterns, but the asymmetry changes with environments. Photosynthetic asymmetry was have been intensively studied for their role in light use efficiency, but less is know about the impact of light properties on asymmetry. Aimed at the current changing fraction of diffuse light in sky radiation, this study investigated dorsoventral asymmetry of photosynthetic traits in direct, diffuse and self-transmitted light (residual light intercepted by one surface) respectively in an important food and energy crop, Sorghum bicolor L . An unique designed method was used to investigate the specific gas exchange of two surfaces in different light properties. We found that anatomical and morphological traits were obviously different in sorghum leaves, which might cause the photosynthetic asymmetry, the variation of photosynthetic rates and stomatal conductance was significant between two surfaces in direct and self-transmitted light, but insignificant in diffuse light. The abaxial stomatal sensitivity of single stoma was lower, while the higher stomatal density in abaxial surface compensated the weakness in stomatal sensitivity. Comparing to direct and self-transmitted light, diffuse light reduced the stomatal sensitivity, while the degree of decline was higher in adaxial surface, which caused weak dorsoventral asymmetry in photosynthesis. Taken together, the finding of this study suggested that stomatal sensitivity determined the degree of dorsoventral asymmetry in the susceptibility to light properties. The different stomatal sensitivity regulated photosynthetic variation, which was benefit to remain high photosynthetic rate in high and changing light. The findings provided new insight in to dorsoventral asymmetry and impact of diffuse light on photosynthesis in isobilateral leaves.