Subsoiling Tillage Promoted Organic Carbon Accumulation by Modifying Soil Structure and Bacterial Community Diversity

ABSTRACT Tillage measures in the summer fallow phase cause soil disturbance and affect the vertical distribution of crop straw, thereby influencing variations in soil microbial structure and soil organic carbon (SOC). However, the specific mechanisms through which soil bacterial communities mediate SOC sequestration remain unclear. Therefore, we investigated the effects of no tillage (FNT), subsoiling tillage (FST), and plowing practice (FPT) in the summer fallow phase on soil properties, SOC stocks, soil extracellular enzymes, and bacterial community structures and functions. This study also identified the dominant factors in SOC accumulation processes. The results indicated that compared with FNT and FPT, FST significantly increased the 0–50 cm soil layer of SOC stock (7.6%–12.3%) due to the increase in the 0–30 cm soil depths. As well, FST markedly increased the soil amylase, β‐xylosidase, lignin peroxidase, β‐glucosidase, and sucrase activities at the 30–40 cm soil depth. These outcomes primarily stem from improvements in soil properties (e.g., mean weight diameter and geometric mean diameter). FNT and FST dramatically enhanced the bacterial community alpha diversity across the 30–40 cm soil layer compared with FPT. Partial least squares path modeling quantified the effects on SOC accumulation; soil water content exerted a significant negative effect (path coefficient, r = −0.249), whereas the mean weight diameter of soil aggregates ( r = 0.354) and bacterial community alpha diversity ( r = 0.603) exerted significant positive effects. Collectively, these factors moderate soil extracellular activities and affect SOC accumulation. Hence, subsoiling tillage in the summer fallow phase significantly improved soil structure, altered bacterial community diversity, and promoted the secretion of soil extracellular enzymes, thereby improving the carbon sequestration capacity. These results expand our understanding of the mechanisms underlying microbe‐mediated carbon sequestration in dryland agriculture.