Soil Profile Effects on Bacterial Diversity and Assembly Under Rotation–Tillage Management on China's Loess Plateau

ABSTRACT

Bacteria are ubiquitous in soil and play an important role in biogeochemical processes. However, most studies on soil bacterial communities have focused on the upper soil layer (0–0 cm), and relatively few studies have focused on deep soil bacterial communities, especially in agroecosystems. This study investigated soil bacterial communities across a 0–100 cm profile (five layers) under crop rotations (maize‐wheat vs. soybean‐wheat) and tillage practices (chisel vs. plow tillage) in semiarid Loess Plateau farmlands using high‐throughput sequencing. Soil depth exerted stronger control over bacterial communities than agricultural management. Soil bacterial community α‐diversity showed a unimodal trend across the soil profile, with the Shannon index peaking at 20–40 cm and the Chao1 index at 40–60 cm, and this pattern was consistent across different management practices. The relative abundances of Proteobacteria, Actinobacteria, and Bacteroidetes were higher in the upper soil layer, while the relative abundances of Acidobacteria, Gemmatimonadetes, Chloroflexi, and Nitrospirae were higher in the deeper soil layers. Both soybean‐wheat pattern and chisel plow tillage practice reduced the complexities of soil bacterial community co‐occurrence patterns, while the complexities of community co‐occurrence patterns showed a unimodal trend throughout the soil profile, with the highest complexity observed at the 60–80 cm layer. Additionally, the soybean‐wheat pattern and chisel plow tillage practice decreased the contribution of deterministic process to soil bacterial community assembly, while the contribution of deterministic process increased with soil depth. Meanwhile, soil physicochemical properties were closely related to the diversity and assembly processes of bacterial communities. Our study reveals bacterial community diversity dynamics and assembly drivers across soil profiles in semiarid farmlands.