Rhizosphere soil bacterial communities response to elevated ozone and nitrogen addition
In this study, the effects of elevated O3 alone, N addition, and their combination on the bacterial community structure of rhizosphere soil of hybrid polar 107 were assessed by using MiSeq sequencing of bacterial 16S rRNA gene. Potted trees were subjected singularly and in combination to two chronic O3 treatments and two nitrogen level in open-top chambers (OTCs). It was found that elevated O3 and its combination with N addition significantly decreased bacterial abundance. Only N addition remarkably decreased the alpha diversity. N addition and its combination with elevated O3 separated the composition of bacterial communities, with an obviously increase in the relative abundances of Protebacteria and Bacteroidetes and a markedly decrease in abundance of Firmicutes. The ecological network based on analysis of topological indices further highlighted the different co-occurrence pattern of the bacterial community in response to N addition, elevated O3, and their combination separately. Elevated O3 and its combination with N addition led to instability of the bacterial community by complicating and centralizing the co-occurrence network and shifting the hub species from RB41 to Bacillus and Blastococcus respectively. On the contrary, N addition stabilized the bacterial community by simplifying and decentralizing the co-occurrence network. The above findings demonstrate that the rhizosphere bacterial community exhibits divergent responses to elevated O3 and N addition respectively. This information highlights the needs to consider the stability of the belowground ecosystem to optimize the plantations management in response to environmental changes.