5:15 PM - 6:30 PM
[HTT16-P11] Evaluation of air pollution stress in roadside trees using stable carbon isotope ratio
Keywords:photosynthesis, stomata, water use efficiency
In Japan, the problem of air pollutants, especially nitrogen oxides, emitted from automobiles and other vehicles became apparent as "urban- and lifestyle-type" air pollution in the 1970s. In Japan in the year of 2021, the amount of nitrogen dioxide in the air has been steadily decreasing in general, but in areas with heavy traffic, the amount of nitrogen dioxide can exceed the environmental standard concentration. Therefore, air pollution in cities is not a problem of the past in Japan. On the other hand, since the 2000s, the amount of nitrogen oxides in the atmosphere has been dramatically increasing in the Asian region along with the remarkable economic growth of China and India, causing serious air pollution problems.
Roadside trees planted in cities have many benefits, such as absorption and trapping of air pollutants in the canopy, suppression of high temperatures through canopy shade formation, and absorption of carbon dioxide through photosynthesis. Since photosynthesis is a physiological function that supports the growth and survival of roadside trees, maintaining photosynthetic activity is essential for the survival of trees in urban areas, which are harsh environments. However, photosynthetic activity is extremely sensitive to various stresses, including air pollution. In particular, the stomata, which uptake carbon dioxide for photosynthesis, close quickly when stressed, resulting in reduced photosynthesis. In order to maintain the photosynthetic function of roadside trees, it is necessary to develop technology that can evaluate the function of the stomata of planted roadside trees in the field. Carbon stable isotope fractionation (Δ13C) of photosynthetic products in leaves has been found to reflect average stomatal openness and has been widely used to determine stress in plants in the natural environment, but there are limited examples of studies applying it to plants in urban areas.
In this presentation, we report the results of a survey conducted from 2007 to 2019 to evaluate the air pollution stress of roadside trees. Rhododendron x pulchrum (R. pulchrum) and Ginkgo biloba (G. biloba) were selected for the study. The R. pulchrum is the most widely used roadside shrub tree species in Japan. Since it is evergreen and often trimmed to within about one meter in height, it is very susceptible to the effects of automobile exhausts. G. biloba is the most widely used tree species in Japan as a tall roadside tree. G. biloba is a deciduous species, with its height is often trimmed to less than 20 meters in urban areas.
The study was conducted as follows:
(1) Twenty-one locations were selected in Kyoto City where traffic volumes and concentrations of nitrogen oxides in the air were different.
(2) Branches of R. pulchrum and G. biloba were collected, and the photosynthetic function of the leaves was analyzed in detail in 2016 and 2017.
For the calculation of Δ13C, the stable carbon isotope ratio of carbon dioxide in the atmosphere was used as a correction. For the amount of nitrogen oxides, we used values from a database provided by the National Institute of the Environmental Studies.
4) Using the data of traffic volume and 3), we mapped Δ13C of R. pulchrum in Kyoto City.
Photosynthesis data analysis for 2016-2017 revealed that the photosynthetic rate of R. pulchrum was lower at study sites with higher concentrations of air pollutants, while the rate of photosynthesis of G. biloba was higher at study sites with higher concentrations of air pollutants. The analysis of the annual data from 2007 to 2019 showed that the Δ13C of R. pulchrum was decreased with higher atmospheric nitrogen dioxide concentration. This indicates that the higher the nitrogen dioxide concentration in the air, the smaller the stomatal opening of the R. pulchrum, indicating that the high nitrogen dioxide concentration imposes a stress to R. pulchrum. On the other hand, the Δ13C of G. biloba was almost constant regardless of the nitrogen dioxide concentration, indicating that the effect of nitrogen dioxide on the stomatal behavior was small. Mapping of Δ13C for R. pulchrum showed that the stomatal opening of R. pulchrum was reduced mainly due to the effect of automobile exhaust at the area around Kyoto Station where the traffic volume was particularly high.
Roadside trees planted in cities have many benefits, such as absorption and trapping of air pollutants in the canopy, suppression of high temperatures through canopy shade formation, and absorption of carbon dioxide through photosynthesis. Since photosynthesis is a physiological function that supports the growth and survival of roadside trees, maintaining photosynthetic activity is essential for the survival of trees in urban areas, which are harsh environments. However, photosynthetic activity is extremely sensitive to various stresses, including air pollution. In particular, the stomata, which uptake carbon dioxide for photosynthesis, close quickly when stressed, resulting in reduced photosynthesis. In order to maintain the photosynthetic function of roadside trees, it is necessary to develop technology that can evaluate the function of the stomata of planted roadside trees in the field. Carbon stable isotope fractionation (Δ13C) of photosynthetic products in leaves has been found to reflect average stomatal openness and has been widely used to determine stress in plants in the natural environment, but there are limited examples of studies applying it to plants in urban areas.
In this presentation, we report the results of a survey conducted from 2007 to 2019 to evaluate the air pollution stress of roadside trees. Rhododendron x pulchrum (R. pulchrum) and Ginkgo biloba (G. biloba) were selected for the study. The R. pulchrum is the most widely used roadside shrub tree species in Japan. Since it is evergreen and often trimmed to within about one meter in height, it is very susceptible to the effects of automobile exhausts. G. biloba is the most widely used tree species in Japan as a tall roadside tree. G. biloba is a deciduous species, with its height is often trimmed to less than 20 meters in urban areas.
The study was conducted as follows:
(1) Twenty-one locations were selected in Kyoto City where traffic volumes and concentrations of nitrogen oxides in the air were different.
(2) Branches of R. pulchrum and G. biloba were collected, and the photosynthetic function of the leaves was analyzed in detail in 2016 and 2017.
For the calculation of Δ13C, the stable carbon isotope ratio of carbon dioxide in the atmosphere was used as a correction. For the amount of nitrogen oxides, we used values from a database provided by the National Institute of the Environmental Studies.
4) Using the data of traffic volume and 3), we mapped Δ13C of R. pulchrum in Kyoto City.
Photosynthesis data analysis for 2016-2017 revealed that the photosynthetic rate of R. pulchrum was lower at study sites with higher concentrations of air pollutants, while the rate of photosynthesis of G. biloba was higher at study sites with higher concentrations of air pollutants. The analysis of the annual data from 2007 to 2019 showed that the Δ13C of R. pulchrum was decreased with higher atmospheric nitrogen dioxide concentration. This indicates that the higher the nitrogen dioxide concentration in the air, the smaller the stomatal opening of the R. pulchrum, indicating that the high nitrogen dioxide concentration imposes a stress to R. pulchrum. On the other hand, the Δ13C of G. biloba was almost constant regardless of the nitrogen dioxide concentration, indicating that the effect of nitrogen dioxide on the stomatal behavior was small. Mapping of Δ13C for R. pulchrum showed that the stomatal opening of R. pulchrum was reduced mainly due to the effect of automobile exhaust at the area around Kyoto Station where the traffic volume was particularly high.