Urban Trees Harbor Phyllosphere Microbiomes Enriched in Pollution-Tolerant Taxa.

Urban vegetation can capture airborne particulate matter (PM), but less is known about how particulate pollution is associated with phyllosphere bacterial communities. This study investigated the phyllosphere microbiomes of seven tropical tree taxa growing at urban and rural/forest sites. Urban leaves accumulated more dust and PM-associated elements. Shannon diversity was lower in urban samples, while richness did not differ significantly between the two environments. Overall bacterial community composition showed substantial overlap, although several taxa differed in relative abundance. Urban samples contained higher relative abundances of stress-associated genera, including Sphingomonas, Staphylococcus, Methylobacterium-Methylorubrum, and Hymenobacter. A core set of bacterial taxa was present in both environments. Correlation and multivariate analyses showed associations among PM1, total atmospheric deposition, plant traits, and microbial community patterns. Tax4Fun2 predicted broadly similar functional potential in both environments, with some differences in pathways related to aromatic compound degradation, nutrient cycling, and metal resistance. These functions were inferred from 16S rRNA gene data and do not represent measured metabolic activity. Overall, the study identifies taxonomic and predicted functional patterns in phyllosphere microbiomes from two contrasting environments.