Pine needle pollution microbiome
Urbanisation is associated with distinct phyllosphere bacterial communities, but observational studies cannot separate the effects of air pollution from confounding land-use factors. Here, we used a free-air diesel and ozone enrichment (FADOE) platform to experimentally isolate the effects of realistic levels of ozone (O3) and diesel exhaust on the needle microbiome of Scots pine (Pinus sylvestris). Air pollution treatments significantly shaped community composition (PERMANOVA, R2 = 0.244, p = 0.001). Pairwise comparisons revealed that ozone alone (p = 0.006, R2 = 0.50) and O3+diesel (p = 0.008, R2 = 0.52) drove the strongest shifts relative to ambient controls, whereas diesel treatment alone had no significant effect. Multiple differential abundance analyses identified limited and inconsistent taxon-specific responses under O3 exposure. These experimentally isolated pollution effects were subtler than those reported in urban vs. non-urban observational studies, suggesting that land-use factors (e.g. temperature changes, habitat fragmentation and heterogeneity) dominate urban phyllosphere microbiome restructuring. By decoupling air pollution from land-use confounders, our findings reframe the relative importance of atmospheric stressors in global change microbiology and highlight ozone as a key driver among air pollutants.
Urbanisation is associated with distinct phyllosphere bacterial communities, but observational studies cannot separate the effects of air pollution from confounding land-use factors. Here, we used a free-air diesel and ozone enrichment (FADOE) platform to experimentally isolate the effects of realistic levels of ozone (O3) and diesel exhaust on the needle microbiome of Scots pine (Pinus sylvestris). Air pollution treatments significantly shaped community composition (PERMANOVA, R2 = 0.244, p = 0.001). Pairwise comparisons revealed that ozone alone (p = 0.006, R2 = 0.50) and O3+diesel (p = 0.008, R2 = 0.52) drove the strongest shifts relative to ambient controls, whereas diesel treatment alone had no significant effect. Multiple differential abundance analyses identified limited and inconsistent taxon-specific responses under O3 exposure. These experimentally isolated pollution effects were subtler than those reported in urban vs. non-urban observational studies, suggesting that land-use factors (e.g. temperature changes, habitat fragmentation and heterogeneity) dominate urban phyllosphere microbiome restructuring. By decoupling air pollution from land-use confounders, our findings reframe the relative importance of atmospheric stressors in global change microbiology and highlight ozone as a key driver among air pollutants.