4:30 PM - 4:45 PM
[HTT18-11] Evaluation of air pollution stress in roadside trees using stable carbon isotope ratio - an attempt to detect the effect of industrial activity stagnation by COVID19
Keywords:stable carbon isotope ratio, isotope discrimination, photosynthesis, stomata, water use efficiency, nitrogen dioxide
The problem of nitrogen oxides, an air pollutant emitted by automobiles and other vehicles, became particularly pronounced in urban areas of Japan after 1985. The amount of nitrogen oxides in the atmosphere has been steadily decreasing since the mid-1990s, and in 2019, the atmospheric concentration of nitrogen dioxide in Kyoto City was reduced to nearly 1/3 of its peak level at some monitoring stations. The amount of nitrogen dioxide in the air in urban areas strongly reflects economic and industrial activities as well as regulations such as the Air Pollution Control Law; for example, there was a significant drop in nitrogen dioxide during the Lehman Shock in 2009.
Urban trees planted in cities have many benefits, including the absorption and capturing of air pollutants in their canopy, the suppression of high summer temperatures through green shade formation, and the absorption of carbon dioxide through photosynthesis. Photosynthesis is a physiological function that supports the growth and survival of urban trees, and therefore, maintaining photosynthetic activity is essential for the survival of trees in urban areas. However, the "stomatal pores," which uptake carbon dioxide that is necessary for photosynthesis, close quickly by air pollution stress, resulting in reduced photosynthesis. We focused on the stable carbon isotope fractionation (Δ13C) in leaves as a technique to evaluate the function of stomata in urban trees in the field, and investigated the relationship between air pollution levels and Δ13C. We obtained that the stomatal closure of the urban shrub tree, azalea, was accompanied by an increase in the amount of nitrogen dioxide due to the increase in traffic amount. In other words, the adverse effect of atmospheric nitrogen dioxide on the photosynthetic function was clearly observed. On the other hand, the Δ13C of the tall tree, ginkgo, was almost constant in response to changes in atmospheric nitrogen dioxide concentration, suggesting that the effect of air pollutants on the photosynthetic function was limited.
The COVID19 epidemic has caused a decline in economic and industrial activities in Japan. This may lead to a decrease in the amount of nitrogen dioxide in the atmosphere, and consequently mitigate the loss of photosynthetic function of urban trees that are sensitive to air pollutants. Since we have been conducting Δ13C analysis by collecting leaves of urban trees in Kyoto and other urban areas intermittently from 2005 to 2021, we may be able to detect how the decline in economic and industrial activities caused by COVID19 affected the photosynthetic function of urban trees by tracking the change of Δ13C of leaves. It may be possible to detect how the COVID19-induced decline in economic and industrial activity affected the photosynthetic function of urban trees.
The methods and objectives of the study are as follows
(1) Selection of study sites, mainly in Kyoto City from 2005 to 2020, where traffic volumes differ and where concentrations of nitrogen oxides in the air are expected to differ
In the calculation of Δ13C, the carbon stable isotope ratio of carbon dioxide in the atmosphere will be used as a correction. The amount of nitrogen oxides will be calculated from the database provided by the National Institute for Environmental Studies.
The analysis of nitrogen dioxide concentrations in Kyoto City from 2005 to 2021 shows that there was a significant drop in 2009, the year of the Lehman Shock, and also in 2020 and 2021 at stations with particularly high traffic volumes, indicating the impact of COVID19. However, the decrease in nitrogen dioxide concentration in 2020 and 2021 was less distinct than that in 2009. We plan to conduct Δ13C analysis of leaves to determine whether COVID19 alleviates the negative effects on photosynthetic function.
Urban trees planted in cities have many benefits, including the absorption and capturing of air pollutants in their canopy, the suppression of high summer temperatures through green shade formation, and the absorption of carbon dioxide through photosynthesis. Photosynthesis is a physiological function that supports the growth and survival of urban trees, and therefore, maintaining photosynthetic activity is essential for the survival of trees in urban areas. However, the "stomatal pores," which uptake carbon dioxide that is necessary for photosynthesis, close quickly by air pollution stress, resulting in reduced photosynthesis. We focused on the stable carbon isotope fractionation (Δ13C) in leaves as a technique to evaluate the function of stomata in urban trees in the field, and investigated the relationship between air pollution levels and Δ13C. We obtained that the stomatal closure of the urban shrub tree, azalea, was accompanied by an increase in the amount of nitrogen dioxide due to the increase in traffic amount. In other words, the adverse effect of atmospheric nitrogen dioxide on the photosynthetic function was clearly observed. On the other hand, the Δ13C of the tall tree, ginkgo, was almost constant in response to changes in atmospheric nitrogen dioxide concentration, suggesting that the effect of air pollutants on the photosynthetic function was limited.
The COVID19 epidemic has caused a decline in economic and industrial activities in Japan. This may lead to a decrease in the amount of nitrogen dioxide in the atmosphere, and consequently mitigate the loss of photosynthetic function of urban trees that are sensitive to air pollutants. Since we have been conducting Δ13C analysis by collecting leaves of urban trees in Kyoto and other urban areas intermittently from 2005 to 2021, we may be able to detect how the decline in economic and industrial activities caused by COVID19 affected the photosynthetic function of urban trees by tracking the change of Δ13C of leaves. It may be possible to detect how the COVID19-induced decline in economic and industrial activity affected the photosynthetic function of urban trees.
The methods and objectives of the study are as follows
(1) Selection of study sites, mainly in Kyoto City from 2005 to 2020, where traffic volumes differ and where concentrations of nitrogen oxides in the air are expected to differ
In the calculation of Δ13C, the carbon stable isotope ratio of carbon dioxide in the atmosphere will be used as a correction. The amount of nitrogen oxides will be calculated from the database provided by the National Institute for Environmental Studies.
The analysis of nitrogen dioxide concentrations in Kyoto City from 2005 to 2021 shows that there was a significant drop in 2009, the year of the Lehman Shock, and also in 2020 and 2021 at stations with particularly high traffic volumes, indicating the impact of COVID19. However, the decrease in nitrogen dioxide concentration in 2020 and 2021 was less distinct than that in 2009. We plan to conduct Δ13C analysis of leaves to determine whether COVID19 alleviates the negative effects on photosynthetic function.