Microbial associations with soil organic carbon pool composition and stabilization in eroding landscapes

Abstract

The persistence of soil organic carbon (SOC), particularly in deeper soils, plays a crucial role in global carbon storage and sequestration. However, the microbial mechanisms underlying carbon sequestration in eroding agricultural landscapes remain unclear. This study investigated SOC formation pathways of under soil erosion, focusing on dissolved organic carbon (DOC) and microbial necromass carbon (MNC), and mineral-associated organic carbon (MAOC) in the topsoil (0–20 cm) versus subsoil (80–100 cm). Results showed that SOC mineralization rates were significantly lower at depositional compared to eroding sites, with reductions of 40.7 % in topsoils and 70.6 % in subsoils. This decline correlated with synergistic alterations in DOC chemistry and microbial processes. At depositional zones, enrichment of aromatic recalcitrant DOC alonged with a 233.6 % increase in subsoil microbial necromass carbon (MNC), where fungal-derived residues became the dominant contributor to MAOC stabilization. Microbial life-strategy reorganization drove these changes, with depositional topsoils showing increased abundances of r-strategist Proteobacteria (+24.0 %) and Gemmatimonadota (+27.4 %)—groups that facilitate rapid substrate utilization—while K-strategist Acidobacteriota decreased by 47.9 %. Although microbial carbon use efficiency was slightly higher at depositional locations, mineral protection of necromass and persistence of aromatic DOC emerged as the primary stabilization mechanisms. Thus, erosion–deposition vertically redistributes SOC persistence through microbially mediated necromass accumulation and mineral complexation, necessitating the integration of microbial functional traits into stratified carbon models.