A Reasonable Rotation Fallow Mode Enhances the Complexity of the Soil Bacterial Network and Enriches Nitrogen-Cycling-Related Taxa.

Rotation fallow is an effective way to overcome the obstacles associated with continuous cropping, being beneficial for the growth and development of crops. Soil micro-organisms are closely related to soil fertility, plant productivity, soil pathogenic bacteria, and crop health in agricultural ecosystems. To explore the effects of different rotation fallow modes on the diversity and functions of the soil bacterial community, a study was conducted in an arid area in the western foothills of the Greater Khingan Mountains. Using spring wheat variety Longmai 36 as the research material, this study systematically analyzed the changes and functional differences in soil physicochemical and biological characteristics, as well as microbial communities (endosphere, rhizosphere, and bulk soil) in spring wheat fields under five rotation fallow modes: Wheat²⁰¹⁶–Wheat²⁰¹⁷–Wheat²⁰¹⁸(WWW), Wheat²⁰¹⁶–Rape²⁰¹⁷–Fallow²⁰¹⁸(WRF), Wheat²⁰¹⁶–Potato²⁰¹⁷–Fallow²⁰¹⁸(WPF), Wheat²⁰¹⁶–Fallow²⁰¹⁷–Rape²⁰¹⁸(WFR), and Wheat²⁰¹⁶–Fallow²⁰¹⁷–Potato²⁰¹⁸ (WFP). The results indicate that, compared to WWW, the soil urease activity, microbial biomass nitrogen content, and microbial biomass phosphorus content were significantly increased in the WFP mode (p < 0.05). In particular, the soil moisture content, organic matter, and total potassium content were increased by 6.88%, 3.34%, and 25.57%, respectively. The Shannon index and chao1 index of bulk soil (BS) and rhizosphere (RS) bacteria were significantly higher than those of endosphere (ER) bacteria (p < 0.05). Both ecological niche and rotation fallow modes affected the relative abundance of dominant bacteria, and the relative abundance of beneficial bacteria, such as Bacteroidetes, Firmicutes, and Verrucomimicrobia, significantly increased in the rotation fallow modes. The complexity and stability of bacterial networks, and abundance of nitrogen-cycling-related functional taxa were significantly improved, while the abundance of pathogen-related functional taxa was significantly decreased. The differences in soil bacterial community structure were closely related to soil physicochemical properties. Compared to ER, BS and RS bacterial communities, which are more susceptible to soil physicochemical properties, and soil pH are key driving forces for bacterial community distribution. In summary, compared with continuous cropping, the rotation fallow mode is beneficial for conserving soil moisture and nutrients, stabilizing soil pH, (i.e., making the soil tend to be neutral), increasing the abundance of beneficial bacteria in the soil, enhancing the complexity and stability of microbial ecological networks, and increasing the abundance of nitrogen-cycling-related functional taxa, thus improving crop growth and development. [ABSTRACT FROM AUTHOR]