Long-term elevated CO2 and warming alter the network complexity and composition of bacterial community in a paddy field

Abstract

Global climate change is mainly characterized by warming and an elevated atmospheric CO₂ concentration, which can affect soil microbial communities. However, the interactive effects of warming and elevated CO₂ on the composition, diversity, function and network complexity of bacterial communities remain unclear. In this study, a long-term open field experiment was conducted to investigate the interactive effects of warming (+2 °C) and CO₂ enrichment (500 ppm) on the bacterial community in a Chinese paddy field. When averaged over the three stages, warming and elevated CO₂ had no individual or interactive effect on the alpha diversity indices of the soil bacterial community. However, elevated CO₂ showed stronger effects on the bacterial community structure than warming, with a significant increase in the relative abundance of the phylum Actinobacteria by 17.5 % and a decrease in Chloroflexi by 15.1 %. Soil organic carbon, pH, total nitrogen and available nitrogen were identified as significant environmental variables for the structuring bacterial community. Co-occurrence network analysis showed that warming significantly increased the network complexity of the soil bacterial community, suggesting that warming enhances the competition of bacterial species interactions. Additionally, the positive effects of warming on the network complexity were moderated by elevated CO₂, in which the network complexity was substantially simplified. Furthermore, elevated CO₂ showed greater effects than warming on the metabolic function of the bacterial community. The COG (clusters of orthologous groups) classifications of posttranslational modification, replication, cell biogenesis and cycle control were significantly increased under elevated CO₂, but those of transcription and secondary metabolite biosynthesis were reduced compared to the ambient control. Overall, these results indicate that the interactive effects of long-term elevated CO₂ and warming will alter the structure composition, network complexity and functioning of soil bacterial communities, and potentially threaten the function of agroecosystems under future climate change scenarios.