Difference in photosynthetic responses to free air ozone fumigation between upper and lower canopy leaves of Japanese oak (Quercus mongolica var. crispula) saplings

Abstract

To clarify the difference of ozone (O3) sensitivity of photosynthesis in leaves located different canopy positions, we investigated photosynthetic responses of Japanese oak saplings to free air O3 exposure, and compared the results with Siebold’s beech saplings reported previously. The O3 at 60 nmol mol-1 during daytime was fumigated for two growing seasons, from 6 August to 11 November 2011 and from 17 May to 10 November 2012. In June, August and October of 2012, we determined photosynthetic activity of upper and lower canopy leaves. The exposure to O3 increased the ratio of intercellular CO2 concentration to ambient CO2 concentration in October, indicating stomatal sluggishness. We observed an O3-induced, significant decrease in light-saturated net photosynthetic rate (Asat) with no significant interaction between O3 effect and canopy position for Asat. Therefore, we conclude that the O3 sensitivity of photosynthesis in upper and lower canopy leaves was similar in Japanese oak, while our previous study reported that the upper canopy leaves of Siebold’s beech have a higher O3 sensitivity than lower canopy leaves.