Responses of photosynthesis and long-term water use efficiency to ambient air pollution in urban roadside trees

Mayu Matsumoto,Luisa Kumpitsch,Takashi Kiyomizu,Atsushi Kume,Tomomitsu Kinoshita,Yuko T Hanba,Saya Yamagishi

doi:10.1007/s11252-022-01212-z

Mayu Matsumoto, Luisa Kumpitsch + Show 5 more

Open Access

https://doi.org/10.1007/s11252-022-01212-z

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Abstract

We conducted on-site studies in Kyoto City, Japan, to evaluate the effect of air pollution by automobile gas exhaust on the leaf photosynthetic functions of four urban roadside tree species. Nitrogen oxides (NO and NO2) are major air pollutants that are related to automobile gas exhaust. The species-specific response of leaf photosynthesis to air pollution was obtained for single-year data, in which at the high air pollution sites, Rhododendron × pulchrum, Rhaphiolepis indica, and Prunus × yedoensis had a higher restriction of maximum photosynthesis (Amax), while the opposite trend was obtained for Ginkgo biloba. When the data were pooled across the years from 2007 to 2019 in R. pulchrum, the dose-dependent effect of NO and NO2 on photosynthesis became obvious, in which they decreased Amax and increased the long-term leaf water use efficiency. A spatial variability map for R. pulchrum showed a lower Amax and higher water use efficiency at the heavy traffic areas in Kyoto City, which suggests that R. pulchrum increased tolerance to air pollution and water stress at the expense of the leaf photosynthesis. This study revealed the importance of the evaluation of the species-specific response of photosynthesis to air pollution for the efficient use of urban trees, even in regions with relatively low atmospheric pollution levels such as < 40 ppb of NO or NO2.

Highlights

The urban environment imposes distinct multiple environmental stresses on trees compared to trees grown in non-urban areas
These results indicate that NO and NO2 are major air pollutants related to automobile gas exhaust in Kyoto City, and that the differences in photosynthetic responses among study sites in Kyoto City would be strongly affected by the levels of NO and NO2
Atmospheric NO and NO2 are important air pollutants that affect the photosynthesis of roadside trees in urban areas

Summary

Introduction

The urban environment imposes distinct multiple environmental stresses on trees compared to trees grown in non-urban areas. Air pollution by traffic exhaust reduces photosynthesis in Pinues densiflora (Kume et al 2000), Platanus occidentalis (Woo and Je 2006), and Rhododendron pulchrum (Kiyomizu et al 2019), and increases photosynthesis in Ilex rotunda (Takagi and Gyokusen 2004), Acer rubrum (Lahr et al 2018), and Ginkgo biloba (Kiyomizu et al 2019). Such diverse responses are affected by species-specific responses to multiple air pollutants. Urban roadside trees are expected to improve air quality by capturing particulate air pollutants, such as PM2.5

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