Particulate matter and polycyclic aromatic hydrocarbon uptake in relation to leaf surface functional traits in Mediterranean evergreens: Potentials for air phytoremediation

We explored relationships between particulate matter (PM) and polycyclic aromatic hydrocarbon (PAHs) leaf concentrations, uptake rates and leaf surface functional traits in four Mediterranean evergreen trees (Chamaerops humilis, Citrus x aurantium, Magnolia grandiflora, and Quercus ilex) during a dry month. Pollutant leaf concentration at different dates and uptake rate were correlated. We quantified PM by gravimetric analysis, PAHs were extracted from intact and dewaxed leaves and analyzed by GC-MS, and cuticle thickness, number and surface of stomata (Ns and SS) and trichomes (N-t and S-t) were determined by optical microscopy. Infrared spectroscopy was used to investigate the leaves surfaces composition and assess esterification index (E). Studied species were characterized by unique combinations of functional traits and pollutant uptake capacities. PM10 uptake scaled positively with S-S, S-t and upper cuticle thickness (T-c,T-u) across species. PM2.5 uptake scaled positively with T-c,T-u, and thicker cuticles were also associated with greater shares of uptake of hydrophobic PM fractions. Uptakes of different fractions of PAH were generally weakly related to different leaf functional traits, except for some correlations with E and S-S. We conclude that both plant surface morphological and chemical leaf traits influence PM and PAH retention, unveiling their potential role in air phytoremediation.