Assessing synergistic effects of crop rotation pattern, tillage practice, and rhizosphere effect on soil bacterial community structure and assembly in China's Loess Plateau farmlands

Soil bacterial communities are important soil regulators in agroecosystems. However, few studies have investigated the influences of integrated agricultural management practices on farmland soil bacterial community diversity and assembly processes. In this study, we assessed the impact of crop species (maize and soybean), tillage practice (chisel plow tillage, CPT; zero tillage, ZT; plow tillage, PT), rhizosphere effect (rhizosphere and bulk soils), and their interactions on the soil bacterial communities in Loess Plateau farmlands. Conservation tillage significantly increased soil moisture (SM), clay and sand fractions, and carbon and nitrogen levels; whereas silt fraction and pH decreased. Rhizosphere effect significantly improved soil texture and decreased SM, pH, total nitrogen, and nitrate nitrogen. Soybean cultivation significantly increased SM, silt fraction, and pH; while clay fraction decreased. Additionally, the rhizosphere effect decreased the competition among rhizosphere bacterial communities (edges: rhizosphere = 926, bulk = 1095; density: rhizosphere = 0.157, bulk = 0.184) and increased the structural complexity of the community network (modularity: rhizosphere = 0.857, bulk = 0.556); moreover, conservation tillage and soybean cultivation increased community network complexity (modularity: CPT = 0.879, ZT = 0.742, PT = 0.495; maize = 0.525, soybean = 0.888). Although the phylogenetic clustering of rhizosphere bacterial communities caused by the rhizosphere effect was lower than that of bulk soil bacterial communities (2.13%), it had no significant influence on rhizosphere or bulk soil bacterial community assembly, and deterministic processes dominated the formation of soil bacterial community structure. In conclusion, clarifying the variations in soil bacterial communities under integrated agricultural management practices can help predict trends in soil bacterial community function which can, in turn, effectively guide biological management decision-making in farming operations. Our findings may provide additional insights into the underground processes in farmland and facilitate the development of conservation farming operations as sustainable agricultural practices.