Simplifying network complexity of soil bacterial community exposed to short-term carbon dioxide and ozone enrichment...

Global atmospheric changes are characterized by increases in carbon dioxide (CO₂) and ozone (O₃) concentrations, with important consequences for the soil microbial community. However, the influences of CO₂ and O₃ enrichment on the biomass, diversity, composition, and functioning of the soil bacterial community remain unclear. We investigated the effects of short-term factorial combinations of CO₂ (by 200 ppm) and O₃ (by 40 ppb) enrichment on the dynamics of soil bacterial community in paddy soils with two rice varieties (Japonica, Nangeng 5055 (NG5055) vs. Wuyujing 3 (WYJ3)) in an open top chamber facility. When averaged both varieties, CO₂ and O₃ enrichment showed no individual or combined effect on the abundance or diversity of soil bacterial community. Similarly, CO₂ enrichment did not exert any significant effect on the relative abundance of bacterial phyla. However, O₃ enrichment significantly reduced the relative abundance of Myxococcota phylum by a mean of 37.5%, which negatively correlated to root N content. Compared to ambient conditions, soil bacterial community composition was separated by CO₂ enrichment in NG5055, and by both CO₂ and O₃ enrichment in WYJ3, with root N content identified as the most influential factor. These results indicated that root N was the top direct predictor for the community composition of soil bacteria. The COG (cluster of orthologous groups) protein of cell motility was significantly reduced by 5.8% under CO₂ enrichment, and the COG protein of cytoskeleton was significantly decreased by 14.7% under O₃ enrichment. Furthermore, the co-occurrence network analysis indicated that both CO₂ and O₃ enrichment decreased the network complexity of the soil bacterial community. Overall, our results highlight that continuous CO₂ and O₃ enrichment would potentially damage the health of paddy soils through adverse impacts on the associations and functional composition of soil microbial communities.