Low soil carbon saturation deficit limits the abundance of cbbL-carrying bacteria under long-term no-tillage maize cultivation in northern China

The responses of cbbL-carrying bacteria to different levels of soil carbon saturation deficits (SCSD) under tillage managements are largely unknown. We assessed the influence of SCSD on the abundance and diversity of cbbL-carrying bacteria under long-term no-tillage with residue retention (NT) and conventional tillage without residue retention (CT) cultivation systems in maize. We found SCSD was smaller under NT than under CT in the 0–15 cm soil layer. The abundance and the Shannon diversity of cbbL-carrying bacteria in the NT treatment were lower than in the CT treatment. Soil carbon saturation and cbbL gene abundance showed a significant positive correlation, but there was no correlation between soil carbon saturation and cbbL gene diversity. However, the long-term NT practice decreased cbbL-carrying bacteria diversity and altered the community structure of the cbbL-carrying bacteria. Our results indicated that low SCSD limited the abundance of cbbL-carrying bacteria, but there was no relationship between low SCSD and diversity of cbbL-carrying bacteria. We suggest that further studies of cbbL-carrying bacteria carbon sequestration rates and capacity should be based on the effect of management practices on cbbL-carrying bacteria abundance and diversity. Our study has important implications for the relationship between the biological and physicochemical mechanisms in CO₂ fixation.