Photosynthetic responses to ozone of upper and lower canopy leaves of Fagus crenata Blume seedlings grown under different soil nutrient conditions.

We aimed to clarify the effects of ozone (O) on photosynthetic ability of upper and lower canopy leaves of Fagus crenata Blume seedlings grown under different soil nutrient conditions. To accomplish this objective, we analyzed the response of photosynthetic parameters such as maximum carboxylation rate (V) to cumulative stomatal O uptake (ΣF) and reduction rate of V per unit ΣF as an index of detoxification capacity for O. The seedlings of Fagus crenata were grown for two growing seasons (2014-2015) in nine treatments comprised of a combination of three levels of gas treatments (charcoal-filtered air or 1.0- or 1.5-times ambient O concentration) and three levels of soil nutrient treatments (non-fertilized or a supply of relatively low or high concentrations of compound fertilizer). The nutrient supply significantly increased the degree of O-induced reduction in V in September. However, nutrient supply did not significantly increase ΣF and reduce the detoxification capacity for O. On the other hand, the degree of O-induced reduction in V of upper canopy leaves was higher as compared with that of lower canopy leaves in August due to the higher ΣF. However, the reduction rate of V per unit ΣF in lower canopy leaves was higher than that in upper canopy leaves, indicating lower detoxification capacity for O in lower canopy leaves. Reduction rate of V per unit ΣF over the threshold, which is assumed to be proportional to gross photosynthetic rate, was similar between upper and lower canopy leaves. Therefore, capacity of photosynthetic CO assimilation is likely to be associated with detoxification capacity for O in upper and lower canopy leaves of F. crenata seedlings grown under different soil nutrient conditions.