11:00 AM - 11:15 AM
[HTT16-12] Evaluation of air pollution stress in roadside trees using stable carbon isotope ratio - to detect the effect of industrial activity stagnation and recovery affected by COVID19
Keywords:stable carbon isotope ratio, photosynthesis, air pollutants, stomata, traffic volume
Roadside trees planted along urban roads have many benefits, including the absorption of carbon dioxide through photosynthesis, the absorption and trapping of air pollutants, and the control of high temperatures through the formation of shade crown. Since photosynthesis is the most basic and important function that supports the growth and survival of roadside trees, maintaining photosynthetic activity is essential for the survival of trees in urban areas. However, various stresses specific to the urban environment may reduce the photosynthetic activity of roadside trees. To maximize the benefit of roadside trees, it would be effective to evaluate their photosynthetic function. We have previously assessed the photosynthetic function of roadside trees by estimating the average stomatal opening using carbon stable isotope ratios (delta-13C).
Air pollutants such as nitrogen dioxide (NO2) emitted from automobiles are among the most important factors that affect roadside tree photosynthesis. However, there is currently no established knowledge of what effects appear on roadside tree photosynthesis at the level of NO2 concentrations in urban air. We focused on the stable carbon isotope fractionation of photosynthetic products in leaves and investigated the relationship between air pollution levels and carbon isotope fractionation. We found that the effects of NO2 on photosynthesis differed significantly among the species of roadside trees, and that NO2 had a clear negative effect on photosynthetic function by closing the stomata of azalea trees, while the effect of NO2 on photosynthetic function was limited for the ginkgo trees.
Given these results, it is possible that the adverse effects on photosynthesis may be mitigated for the NO2-sensitive azalea trees if an event occurs in the city that lowers the concentration of atmospheric NO2. The COVID19 pandeic that began in 2020 caused a global decline in industrial activity, including Japan. According to traffic censuses conducted in 2015 and 2021, heavy vehicle traffic was about 19% lower in 2021 than in 2015. On the other hand, since early 2023, the impact of COVID19 has been mitigating and industrial activity has been recovering.
In order to investigate how such changes in NO2 concentrations due to the stagnation and recovery of industrial activity caused by COVID19 are manifested in the photosynthetic function of roadside tree leaves, the following studies were conducted.
1. Selected study sites, mainly in Kyoto City from 2005 to 2023, where traffic volumes differ and concentrations of atmospheric NO2 are expected to differ.
2. Leaves of azalea trees, tall cherry trees and Ginkgo trees were collected, and their carbon isotope fractionation was measured to determine the difference in carbon isotope fractionation between the period when COVID19 had an effect and the period without the effect.
First, we analyzed NO2 concentrations in Kyoto City from 2005 to 2023, and found that there was a drop in 2020, 2021, and 2022, especially at the air pollutant monitoring stations with high traffic volumes, indicating that the impact of COVID19 was manifested as a decrease in NO2 concentrations. On the other hand, in 2023, the depression of NO2 concentration was somewhat mitigated. Leaf carbon isotope fractionation analysis was performed to compare the carbon isotope fractionation from 2020-2023, which was affected by COVID19, with the carbon isotope fractionation from the period when COVID19 had no effect. The results indicated that NO2-induced stomatal closure may have been alleviated during 2020-2023 in the azalea trees. On the other hand, when comparing 2020-2022 with 2023, we expected to see the effect of industrial activity recovery in 2023, but carbon isotope fractionation values did not clearly show such an effect. In the presentation, we will also report the results of similar analyses for other tree species such as cherry trees and Ginkgo trees.
This research was supported by Grant-in-Aid for Scientific Research 19H04281, 23H0552, and the Kyoto Knowledge Industry Creation Forest 2023 Industry-Academia Joint Research and Development Project.
Air pollutants such as nitrogen dioxide (NO2) emitted from automobiles are among the most important factors that affect roadside tree photosynthesis. However, there is currently no established knowledge of what effects appear on roadside tree photosynthesis at the level of NO2 concentrations in urban air. We focused on the stable carbon isotope fractionation of photosynthetic products in leaves and investigated the relationship between air pollution levels and carbon isotope fractionation. We found that the effects of NO2 on photosynthesis differed significantly among the species of roadside trees, and that NO2 had a clear negative effect on photosynthetic function by closing the stomata of azalea trees, while the effect of NO2 on photosynthetic function was limited for the ginkgo trees.
Given these results, it is possible that the adverse effects on photosynthesis may be mitigated for the NO2-sensitive azalea trees if an event occurs in the city that lowers the concentration of atmospheric NO2. The COVID19 pandeic that began in 2020 caused a global decline in industrial activity, including Japan. According to traffic censuses conducted in 2015 and 2021, heavy vehicle traffic was about 19% lower in 2021 than in 2015. On the other hand, since early 2023, the impact of COVID19 has been mitigating and industrial activity has been recovering.
In order to investigate how such changes in NO2 concentrations due to the stagnation and recovery of industrial activity caused by COVID19 are manifested in the photosynthetic function of roadside tree leaves, the following studies were conducted.
1. Selected study sites, mainly in Kyoto City from 2005 to 2023, where traffic volumes differ and concentrations of atmospheric NO2 are expected to differ.
2. Leaves of azalea trees, tall cherry trees and Ginkgo trees were collected, and their carbon isotope fractionation was measured to determine the difference in carbon isotope fractionation between the period when COVID19 had an effect and the period without the effect.
First, we analyzed NO2 concentrations in Kyoto City from 2005 to 2023, and found that there was a drop in 2020, 2021, and 2022, especially at the air pollutant monitoring stations with high traffic volumes, indicating that the impact of COVID19 was manifested as a decrease in NO2 concentrations. On the other hand, in 2023, the depression of NO2 concentration was somewhat mitigated. Leaf carbon isotope fractionation analysis was performed to compare the carbon isotope fractionation from 2020-2023, which was affected by COVID19, with the carbon isotope fractionation from the period when COVID19 had no effect. The results indicated that NO2-induced stomatal closure may have been alleviated during 2020-2023 in the azalea trees. On the other hand, when comparing 2020-2022 with 2023, we expected to see the effect of industrial activity recovery in 2023, but carbon isotope fractionation values did not clearly show such an effect. In the presentation, we will also report the results of similar analyses for other tree species such as cherry trees and Ginkgo trees.
This research was supported by Grant-in-Aid for Scientific Research 19H04281, 23H0552, and the Kyoto Knowledge Industry Creation Forest 2023 Industry-Academia Joint Research and Development Project.