The Interactive Effects of Nitrogen Addition and Ozone Pollution on Cathay Poplar-Associated Phyllosphere Bacterial Communities.

Ground-level ozone (O₃) can adversely impact tree productivity and the service functions of forest ecosystems. The deposition of atmospheric nitrogen (N) can enhance nutrient availability and mitigate the O₃-mediated impairment of plant–soil–microbe systems. Interactions between plants and associated microbial communities are integral to the ability of these plants to resist environmental stressors, yet studies examining the impact of increased O₃ and N levels, alone or in combination, on these phyllosphere bacterial communities have been lacking to date. Accordingly, this study was conducted to examine the impact of O₃ (charcoal-filtered air vs. non-filtered ambient air + 40 ppb of O₃), N addition (0, 50, and 100 kg N ha⁻¹ year⁻¹), and a combination of these treatments on the phyllosphere bacterial communities associated with Cathay poplars. Higher O₃ levels were found to significantly reduce the relative abundance of Gammaproteobacteria phyla while increasing the relative abundance of the dominant Alphaproteobacteria and Betaproteobacteria, with these effects being independent of N levels. Consistently, while marked differences in the composition of phyllosphere bacterial communities were observed as a function of O₃ treatment conditions, they were largely similar across N treatments. Higher O₃ levels contributed to significant reductions in α diversity, including both observed OTUs and phylogenetic diversity, when no N or low levels of N were added. α diversity was not affected by the N addition irrespective of O₃ levels. A significant correlation was observed between photosynthesis rates and both α diversity and phyllosphere bacterial community composition, indicating a close relationship between photosynthetic activity and this microbial community. Together, these data offer new ecological insights regarding O₃-induced changes in the makeup of bacterial communities present on plant surfaces, providing a foundation for efforts to formulate novel management strategies aimed at adapting environmental stressors under conditions of O₃ pollution and in N-enriched environments. [ABSTRACT FROM AUTHOR]