PM2.5 reduction capacities and their relation to morphological and physiological traits in 13 landscaping tree species

Fine particulate matter (PM2.5) is emerging as a serious environmental problem worldwide with the increase in anthropogenic emission sources, such as fossil fuels, transportation, and industries. In urban areas, where industrial complexes and human activities are concentrated, PM2.5 poses a threat to human health. Recently, because of their ability to reduce PM2.5, the introduction of landscaping trees as an environment-friendly solution has become popular; however, there remains a lack of research on the selection of species and their management. In this study, we quantified and compared the PM2.5 reduction capacities of 13 major landscaping tree species and analyzed their relationship with the morphological and physiological characteristics of each species. The results showed that the amount of PM2.5 reduction per leaf area differed among species and was the highest in Ginkgo biloba (28 165 +/- 5353 # cm(-2) min(-1)) and the lowest in Pinus strobus (1602 +/- 186 # cm(-2) min(-1)). Moreover, PM2.5 reduction by the broadleaf species (18 802 +/- 1638 # cm(-2) min(-1)) was approximately 8.6-fold higher than that of the needleleaf species (2194 +/- 307 # cm-2 min-1). Correlation analysis revealed that differences in PM2.5 reduction were explained by differences in specific leaf area between species (P = 0.004) and by the length of margin per leaf area among individual trees (P < 0.05). Additionally, reduction in PM2.5 correlated with photosynthetic properties such as maximum assimilation and carboxylation rates (P < 0.001), indicating that PM2.5 is reduced not only by physical adsorption but also by physiological processes. These findings emphasize that for effective reduction in PM2.5 using landscaping trees, comprehensive consideration of the morphological and physiological characteristics of the species is essential during species selection, and that continuous management is also necessary to maintain the active physiological conditions of the trees.