Abstract: Pressure from machinery and continuous agricultural production exacerbate soil compaction. Deep tillage (DT) can reduce subsoil compaction, but the effects of DT on soil bacterial communities at various spatial and temporal scales and the sustainability of tillage effects remain unclear. Here, we collected soil profile samples from 18 farmlands in a multi-cropped upland paddy area in southern China to investigate the current status of soil compaction. DT effects on soil physicochemical properties and bacterial communities at different soil depths were investigated by establishing three long-term experimental sites, and the sustainability of the effects of DT were preliminarily explored. Our results showed that soil compaction occurred at soil depths greater than 20 cm, as evidenced by higher soil bulk density, and sharp decreases in water and nutrient contents and bacterial community diversity. Although the ameliorative effect of DT on deep soil compaction diminished in the fourth year, the water and organic matter content and bacterial α diversity remained high. DT resulted in a more homogeneous bacterial community across the soil profile in terms of community similarity and compositional stability, along with increased alpha diversity, all of which were associated with reduced heterogeneity in soil variables, increased soil organic matter content, and an increase in the importance of homogeneous selection in the community assembly mechanism. Additionally, the homogenization of bacterial communities under DT promoted an enhancement in bacterial network complexity and stability. Collectively, our findings reveal the importance of deep soil improvement on the spatial homogenization of bacterial communities, which has far-reaching implications for comprehensively understanding the mechanisms by which DT affects microbial distribution patterns along a soil profile.

Deep tillage, biotic homogenization, soil compaction, community similarity, microbial assembly mechanism