[HTT23-P12] Influence of atmospheric pollutants on roadside trees in Kyoto city
We selected three study sites in Kyoto city, such as Omiya (35°01'08.N 135°75'20.E), Yamashina (34°97'18.N 135°81'45.E), and Nishinokyo (35°01'83.N 135°73'08.E). These sites were selected according to the NOx concentration in order to compare effects of different levels of O3 on roadside trees. The species investigated were Rhododendron pulchrum and Prunus yedoensis, which are major roadside trees in Kyoto city. Average concentration of O3 were measured twice at study sites, using passive samplers for 7 days in early June and late November in 2016. It is expected that the trees growing in a study area with a high concentration of O3 have more decreased physiological activity. Photosynthetic activity was evaluated by gas exchange parameters using a portable photosynthesis system, Li-6400 (LI-COR). In addition, stable carbon isotope ratios, which are indicators for long-term water use efficiency, were measured using CN-IRMS. In order to identify factors affecting photosynthetic activity, the relationship between environmental and photosynthetic variables were analyzed by Pearson's moment correlation analysis.
O3 concentration in early July was 75.8 ppb at Omiya, 80.8 ppb at Yamashina, and 55.6 ppb at Nishinokyo. The photosynthetic rate of P. yedoensis measured at PPFD of 1500 μmol m-2 s-1 was significantly higher in Yamashina than those in the other study sites. The same tends were obtained for stomatal conductance (gs). Maximum carboxylation rate of Rubisco (Vcmax) and electron transport rate in thylakoid membrane (J) were high in Nishinokyo for R. pulchrum, which suggests that biochemical activity in photosynthesis was high in Nishinokyo in R. pulchrum. Although there was a difference in the photosynthetic activity of these roadside trees between the study sites, correlation analysis showed that there was no correlation between O3 concentration and photosynthetic activity. The carbon isotope discrimination in leaves of R. pulchrum showed high values in Omiya and Yamashina, which suggested that water use efficiency was high at these two sites.
We conclude that O3 concentration was not related to the photosynthetic rate of the roadside trees in Kyoto city. Possibility the concentration of O3 in the all three study sites was not so high as to affect the roadside trees.