The relationship between particulate matter retention capacity and leaf surface micromorphology of ten tree species in Hangzhou, China.

Atmospheric particulate matter (PM) is one of the main environmental air pollutants, but it can be retained and adsorbed by plants. To systematically and comprehensively conduct qualitative and quantitative research on the relationship between the leaf PM retention ability and the microstructure of leaf surfaces, this study evaluated the PM retention abilities of ten common tree species (1860 leaf pieces in total) in the greenbelts around the Lin'an toll station of the Hang-Rui Expressway in Hangzhou, China, in October 2019. The leaf surface roughness and contact angle were measured with confocal laser scanning microscopy and a contact angle measuring instrument. Scanning electron microscopy was applied to collect data on the stomata and groove morphology. The PM retention ability of the leaves was assessed by quantifying the PM mass and number density on the leaves. The results revealed that Platanus acerifolia and Sapindus mukorossi had a strong ability to retain particulates of different sizes. The mass of the retained PM2.5 on their leaves accounted for the lowest proportion (mean: 8.12%) among the total retained particulate mass, but the number density of the retained PM2.5 accounted for the highest proportion (mean: 97.49%) among the total number density. A significant negative correlation between the PM2.5 mass and the groove width on the adaxial surface (R2 = 0.746, P < 0.05) and a significant positive correlation between the roughness and the PM number density on the adaxial surface (R2 = 0.702, P < 0.01) were observed. No obvious correlations were found among the groove width, roughness and number density of the retained PM on the abaxial surface. Leaf surfaces with dense and narrow grooves, strip-like projections, high roughness and high wettability had strong retention abilities. This study can provide a theoretical reference for selecting plants with strong PM retention ability for green urban garden design.