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

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.