Conservation tillage regulates the assembly, network structure and ecological function of the soil bacterial community in black soils

Traditional tillage represents a serious threat to the stability of soil ecosystems. Understanding the response mechanisms of soil microbial community assembly to different tillage practices is a major topic of soil ecological research. Here, we investigated the bacterial community structures and assembly in bulk and rhizosphere soils of soybeans grown under traditional tillage (moldboard plow, MP) and two conservation tillage practices, namely, no-tillage (NT) and ridge tillage (RT), using high-throughput sequencing methods. Compared with MP, NT and RT increased the relative abundances of nitrifying bacteria of Nitrosospira sp. and the nitrogen-fixing bacteria of Mesorhizobium sp., Bradyrhizobium sp. and Burkholderia sp., but decreased the abundance of carbon-degrading bacteria, especially Blastococcus sp., Streptomyces sp. and Sphingomonas sp. The altered functional bacteria were mostly affiliated with biomarkers and keystone taxa in the NT and RT networks. For the results of network properties and assembly processes, we found that NT and RT habited a more stable bacterial network structure and a lower homogenizing dispersal value. Soil pH was the primary factor regulating both the bacterial community structures and assembly processes under the three tillage practices. The soil bacterial community structures and assembly processes were profoundly altered by tillage practices. The changes in functional bacteria indicated that conservation tillage might contribute to soil carbon sequestration, while stimulating nitrogen fixation and nitrification.