## 2 Materials and Methods
### Calculation of POD  
The POD with a flux threshold of Y nmol O\({}_{3}\) m\({}^{-2}\) LA s\({}^{-1}\) (POD\({}_{Y}\), mmol O\({}_{3}\) m\({}^{-2}\) LA), during one growing season, was calculated according to the method described by CLRTAP (2017) and [PERSON] et al. (2014)([PERSON] et al., 2014; [PERSON] et al., 2015), with modifications of the parameters in the stomatal conductance model based on the \(g_{\rm sw}\) obtained in the present study. The period used to calculate the POD\({}_{Y}\) was from the day of leaf emergence of each leaf type to the day on which the net photosynthetic rate was measured for each growing season. The POD\({}_{Y}\) during the daylight hours was calculated by accumulating stomatal O\({}_{3}\) flux (\(F_{\rm st}\), nmol O\({}_{3}\) m\({}^{-2}\) LA s\({}^{-1}\)) with or without a flux threshold of Y nmol O\({}_{3}\) m\({}^{-2}\) LA s\({}^{-1}\) (POD\({}_{Y}\) or POD\({}_{0}\), respectively). The \(F_{\rm st}\) was calculated using the following equation:  
\[F_{\rm st}=\frac{\left[\rm O_{3}\right]_{\rm air}\,-\,\left[\rm O_{3}\right]_{ \rm leaf}}{r_{\rm b\_ozone}\,+\,r_{\rm s\_ozone}} \tag{1}\]  
where [O\({}_{3}\)]\({}_{\rm air}\) and [O\({}_{3}\)]\({}_{\rm leaf}\) represent O\({}_{3}\) concentrations in the air and the intercellular space (nmol O\({}_{3}\) mol\({}^{-1}\)), respectively, and \(r_{\rm b\_ozone}\) and \(r_{\rm s\_ozone}\) represent boundary layer resistance and stomatal resistance for O\({}_{3}\) diffusion, respectively. For each gas treatment, the average hourly mean O\({}_{3}\) concentration of three chambers was used for [O\({}_{3}\)]\({}_{\rm air}\). The [O\({}_{3}\)]\({}_{\rm leaf}\) was assumed to be zero ([PERSON] et al., 2014). The \(r_{\rm b\_ozone}\) was calculated from the crosswind leaf dimension (\(L_{\rm d}\), m) and wind speed (u, m s\({}^{-1}\)) as follows:  
\[r_{\rm b\_ozone}=1.3\times 150\times\sqrt{\frac{L_{d}}{u}} \tag{2}\]  
where the factor 1.3 accounts for the difference in diffusivity between heat and O\({}_{3}\)([PERSON] et al., 2014). Average \(L_{\rm d}\) values for _F. crenata_, _Q. serrata_, _Q. mongolica_ var. _crispula_ and the early and late leaves of _B. platuphylla_ var. _japonica_ seedlings were 0.014, 0.015, 0.023, 0.012 and 0.032 m, respectively. The average wind speed 1.5 m above the OTC floors was 0.17 m s\({}^{-1}\). The \(r_{\rm s\_ozone}\), the reciprocal of the hourly mean stomatal diffusive conductance to O\({}_{3}\) (\(g_{\rm sO3}\), mmol O\({}_{3}\) m\({}^{-2}\) s\({}^{-1}\)), was calculated from the hourly mean \(g_{\rm sw}\) and a conversion factor of 0.663 was used to account for the difference in the molecular diffusivity of O\({}_{3}\) and that of water vapor in air ([PERSON] et al., 2014; [PERSON] et al., 2015). The hourly mean \(g_{\rm sw}\) was estimated using the stomatal conductance model reported by [PERSON] et al. (2014)([PERSON] et al., 2015):  
\[g_{\rm sto}=g_{\rm max}\times f_{\rm phen}\times f_{\rm light}\times\max\left\{ f_{\rm min},\left(f_{\rm temp}\times f_{\rm VPD}\times f_{\rm SWC}\times f_{\rm 0 3 conc}\right)\right\} \tag{3}\]  
where \(g_{\rm sto}\) represents the estimated hourly mean \(g_{\rm sw}\) and \(g_{\rm max}\) represents the species-specific maximum \(g_{\rm sw}\).