## 4 Discussion  
In the present study, we evaluated the negative effects of O\({}_{3}\) on leaf-level photosynthetic CO\({}_{2}\) uptake, which could be easily incorporated into models of the carbon cycling, in the seedlings of four representative Japanese deciduous broad-leaved forest tree species based on POD. [PERSON] et al. (2013) [39] compiled and analyzed the response of \(A_{\text{sat}}\) to POD using data from the peer-reviewed literature. Although the overall decrease in \(A_{\text{sat}}\) was observed, high variance masked any correlations between the decline in \(A_{\text{sat}}\) with increase in POD. Because POD could be related to cumulative O\({}_{3}\) damages, it could correspond not to O\({}_{3}\) effect on net photosynthetic rate at a certain time but to that on cumulative photosynthetic CO\({}_{2}\) uptake. Several researchers observed that the extent of the O\({}_{3}\)-induced reduction in net photosynthetic rate varied seasonally [29; 40]. On the other hand, [PERSON] et al. (1995) [41] observed a greater extent of O\({}_{3}\)-induced reduction in net photosynthetic rate under high light intensities compared with under low light intensities, indicating variations in the extent of the O\({}_{3}\) damage on photosynthetic CO\({}_{2}\) uptake during the daytime and among canopy positions owing to diurnal variation in the light intensity and self-shading, respectively. In the present study, to take such seasonal and diurnal variations into account, we estimated \(\Sigma P_{\text{n\_est}}\) from _A_-light curves measured monthly and diurnal changes in PPFD throughout the entire growing season. Because this estimation assumes that the _A_-light curves have been constant for about one month and ignored the diurnal changes in air temperature and relative air humidity, it was necessary to validate the estimation. For this purpose, we expanded the \(\Sigma P_{\text{n\_est}}\) from a LA basis to the whole-plant basis by considering a roughly estimated LA per plant and whole-plant-level \(\Sigma P_{\text{n\_est}}\) was compared with WDM increment over two growing seasons. Although not all the species showed significant correlations between WDM  
Figure 3: Relationship between the relative value of leaf-level \(\Sigma P_{\text{n\_est}}\) (%) and relative \(\Sigma A_{\text{sat}}\times\text{days}\) (%) in the 1 st flush leaves of _F. crentata_ (_Fc_), the 1 st and 2 nd flush leaves of _Q. serrata_ (_Qs_ 1 st and _Qs_ 2 nd, respectively), the 1 st and 2 nd flush leaves of _Q. mongolica_ var. _crispula_ (_Qm_ 1 st and _Qm_ 2 nd, respectively), and the early and late leaves of _B. platyphylla_ var. _japonica_ (_Bp_ early and _Bp_ late, respectively). Datasets for the charcoal-filtered air (CF) treatment were not plotted. The relationship was analyzed by linear regression. Solid and dashed lines indicate the regression line and 1:1 line, respectively. The equation and the coefficient of determination (\(R^{2}\)) of the regression line are indicated in the figure. Significance for the \(R^{2}\) is shown: \({}^{**}\)\(p<0.001\). increment and the whole-plant-level \(\Sigma P_{\text{n\_est}}\) during the two growing seasons (Figure 1), all the species had relatively high \(R^{2}\) values. In general, whole-plant growth is largely determined by the amount of leaf area per plant and net photosynthetic rate per leaf area. Although the LA per plant was roughly estimated and calculation of \(\Sigma P_{\text{n\_est}}\) did not consider the effects of environmental condition other than light intensity on photosynthetic CO\({}_{2}\) uptake, these results suggest that the leaf-level \(\Sigma P_{\text{n\_est}}\) could reflect the cumulative photosynthetic CO\({}_{2}\) uptake of the seedlings per unit LA, which could be easily incorporated into models of the carbon cycling.