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

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