Fluorescence spectra and Microrganim

Crop residue incorporation is an effective agronomic measure for mitigating cropland quality degradation, yet the short-term pathways of carbon sequestration and underlying microbial mechanisms remain unclear. This study compared the effects of incorporating straw (FS) and root (FR) residues on soil organic carbon (SOC) fractions, molecular structure, and microbial community. Although short-term FS and FR did not significantly alter SOC, particulate organic carbon (POC), or mineral-associated organic carbon (MAOC) content, FR significantly enhanced the proportion of stable carbon forms. Specifically, FR increased polysaccharide-C and aliphatic-C₂ in POC by 30.5% and 24.1%, and in MAOC by 22.9% and 20.0%, respectively. It also raised dissolved organic carbon (DOC) by 2.31% and the humification index (HIX) by 9.66%, with DOC derived mainly from microbial sources. Microbial community shifts under FR showed increased oligotrophic bacteria and fungi by 18.1% and 118.7%, and reduced eutrophic groups by 29.4% and 34.1%. Structural equation modelling revealed that oligotrophs directly facilitated POC formation and indirectly promoted MAOC via enzymatic effects on DOC, while copiotrophs directly dominated MAOC accumulation. These findings underscore FR’s role in promoting carbon stabilization through synergistic microbial and mineral carbon pathways, highlighting the importance of different residues shaping the functional dynamics of soil microbial communities for precision carbon sequestration in future agricultural management.