Leaf Traits Mediate Phyllosphere Bacterial Community Assembly and Their Role in Degrading Traffic-Derived Polycyclic Aromatic Hydrocarbons

Transport emissions are a major source of urban polycyclic aromatic hydrocarbons (PAHs), posing risks to human health. While plant leaves and their epiphytic microbes contribute to PAH degradation, how plant traits and environmental factors affect this process remains unclear. This study examined 20 tree species in Beijing's traffic corridors to explore PAH enrichment on leaves and the structure of phyllospheric bacterial communities. Results show that leaf area, morphology, and sampling height significantly influenced bacterial community assembly. Normalized Stochasticity Ratio (NST) analysis indicated that deterministic processes dominate on medium-sized leaves (11.8-40.1 cm²), simple leaves, and those below 2.3 m or above 3 m in height, whereas stochastic factors prevail on nano leaves, compound leaves, and leaves at low-position (<2.3 m). Although low-molecular-weight PAHs (2-4 rings) were predominant in leaves, Mantel tests revealed significant positive correlations between bacterial communities and high molecular weight PAHs (4-6 rings), such as benz(a)anthracene, benzo[e]pyrene, and picene. Spearman analysis identified 10 dominant bacterial taxa with PAH degradation potential, including <i>Kocuria rosea</i>, <i>Serratia symbiotica</i>, <i>Massilia</i> sp. WG5, and seven unclassified species from <i>Hymenobacter</i>, <i>Sphingomonas</i>, <i>Roseomonas</i>, <i>Curtobacterium</i>, and <i>Deinococcus</i>. Functional Annotation of Prokaryotic Taxa(FAPROTAX) prediction further associated 14 species across six genera, including <i>Acinetobacter</i>, <i>Nocardioides</i>, <i>Gordonia</i>, <i>Rhodococcus</i>, <i>Clostridium_sensu_stricto</i>_18, and <i>Geobacter</i>, with PAH degradation function. This work clarifies the composition and function of phyllospheric PAH-degrading bacteria in an urban traffic environment, offering a theoretical basis for enhancing degradation via bacterial consortia, biosurfactants, and optimized plant selection.