Diversified crop rotations improve soil microbial communities and functions in a six-year field experiment

Diversified crop rotations can help mitigate the negative impacts of increased agricultural intensity on the sustainability of agroecosystems. However, the impact of crop rotation diversity on the complexity of soil microbial association networks and ecological functions is still not well understood. In this study, a 6-year field experiment was conducted to evaluate how six different crop rotations change the composition and network complexity of soil microbial communities, as well as their related ecological functions. Microbial traits were measured in six crop rotations with different crop diversity index (CDI) during 2016–2022, including winter wheat–summer maize (CDI 1, WM) as the control, sweet potato→winter wheat–summer maize (CDI 1.5, SpWM), peanut→winter wheat–summer maize (CDI 1.5, PWM), soybean→winter wheat–summer maize (CDI 1.5, SWM), spring maize→winter wheat–summer maize (CDI 1.5, SmWM), and ryegrass–sweet sorghum→winter wheat–summer maize (CDI 2, RSWM). The study findings indicated that diversified crop rotations significantly increased ASV richness of both bacterial and fungal communities after 6-year treatments, and the β-diversity profiles of bacterial and fungal communities significantly distinguished at the year of 2022 from 2016. The relative abundance of Acidobacteria and Chloroflexi was significantly enriched in SpWM rotation at 2022, while Basidiomycota significantly declined in five diversified rotations compared to WM. Diversified crop rotations at 2022 increased the complexity and density of bacterial and fungal networks than 2016. SpWM and PWM rotations had the highest functional groups involved in chemoheterotrophy and saprotroph, respectively. Structural equation modelling (SEM) also revealed that diversified crop rotations increased soil nutrients through improving the composition of bacterial communities and the augmented intricacy of the interconnections within both bacterial and fungal communities. This research underscores the importance of preserving the diversity and ecological functions of soil microorganisms in the nutrient-recycling processes for efficient agricultural practices.