Leaf traits of Quercus ilex L. affect particulate matter accumulation

Abstract In urban areas, particulate matter (PM) is the most abundant airborne pollutant. Plants have been reported to filter PM, as leaves may intercept and adsorb it. The aims of the research were: i) to evaluate if leaves of Quercus ilex L., an ornamental species proven to be a good monitor of air quality, of different ages (1 and 2 years old) differed for the main leaf traits; ii) to assess the efficiency of Q. ilex L. leaves of different ages to intercept particulate matter of two sizes (PM>10 and PM10); iii) to highlight the leaf traits that enhanced the accumulation of PM>10 and PM10 on leaf surface. The research was performed at four municipalities on the outskirts of Naples (Southern Italy). In April 2018, Q. ilex L. leaves of one and two years old were collected and then described for length, width, area, thickness, circularity, dry matter content and petiole length. The tested hypotheses were: older leaves, that should have high values of the investigated leaf traits, intercept and accumulate greater amounts of PM; leaves with greater circularity, width and length, and with lower dry matter content are expected to accumulate more PM. The findings highlighted that Q. ilex leaves of different ages did not statistically differ neither for the investigated leaf traits nor for the amounts of accumulated PM>10 and PM10; the greater amount of PM was observed in Q. ilex leaves with higher circularity and lower dry matter content; smaller width leaves seem to favour the accumulation of PM>10 and those with smaller length the accumulation of PM10.