Vegetation exposed to traffic exhaust: a dual study of chlorophyll fluorescence kinetics in Platanus x acerifolia and antioxidative responses in Brassica oleracea var. italica

Abstract

Air pollution worldwide is increasing, and it is considered the largest environmental threat to human health. Cities, in particular, have been experiencing worsening air quality, a direct consequence of further urbanization accompanied with an increased traffic load. Urban vegetation is directly exposed to the present air pollution, and has the potential to serve as a bioindicator for poor air quality. This study carried out a comparison of Hasselt's busy inner ring road, and Kapermolen Park outside the city center. We hypothesized that London Planes near Hasselt inner ring road showed altered physiological and structural characteristics compared to those near Kapermolen Park. Results showed a significantly higher presence of Cu, Fe and Pb in leaves from Hasselt inner ring road compared to the reference site, which are all related to traffic exposure. These leaves also show a significantly higher performance index and electron transport rate, which indicates a stress-induced increase in plant performance. Finally, a correlation analysis of the investigated parameters showed a significant association between the specific leaf area and heat dissipation, and the relative chlorophyll content and Cu, Zn, and Ni with some of the parameters of the chlorophyll fluorescence kinetics, the latter of which are all involved in processes of photosynthesis or plant growth and development. We conclude that trees near Hasselt inner ring road indicate a higher overall performance and show more deposition of traffic-related heavy metals.