Urban Pollution Shapes the Endophytic Microbiome of Urban Trees

This study investigated the diversity, composition, and functional potential of endophytic bacterial communities inhabiting the phyllosphere of three common urban tree species: Tilia tomentosa, Fraxinus excelsior, and Pinus nigra. Leaves were sampled from four locations in the city of Plovdiv, Bulgaria, characterised by different levels of environmental pollution. High-throughput 16S rRNA gene sequencing, together with alpha and beta diversity indices, revealed that urban trees host diverse bacterial communities and that local microenvironmental conditions strongly shape microbial community structure. Fraxinus excelsior and Tilia tomentosa harbour more diverse and functionally enriched endophytic microbiomes, with significantly higher relative abundances of beneficial genera such as Microvirga, Brevundimonas, and Arthrobacter. In contrast, Pinus nigra hosts more specialised taxa, including Novosphingobium, which are known for their ability to degrade environmental pollutants.