Abstract
Organic material return (OMAR) and tillage systems are crucial agricultural management practices that govern soil microbial properties and organic carbon (OC) content, thereby fundamentally determining soil fertility. However, the precise mechanisms by which these practices mediate microbial activity to enhance distinct OC fractions remain poorly understood. Through a field experiment, we systematically evaluated changes in OC components and soil microbial properties under four treatments (CT, CTS, NTS, and BC). Results indicated that, compared to the CT treatment, BC significantly increased the concentrations of total organic carbon (TOC), light fraction organic carbon (LFOC), and particulate organic carbon (POC) by 181.9%, 1649.4%, and 2778.6%, respectively. Conversely, NTS and CTS increased the content of labile organic carbon (LOC) by 225.6% and 206.6%, and dissolved organic carbon (DOC) by 9.7% and 21.9%. Furthermore, OMAR significantly altered microbial α-diversity and community structure, driving a proportional increase that favored copiotrophic bacteria, such as Bacteroidetes (26.0%-209.4%), Firmicutes (90.5%-268.4%), and Actinobacteria (2.2%-52.1%), while concomitantly depleting oligotrophic K-strategists, including Alphaproteobacteria (24.9%-39.4%) and Acidobacteria (2.9%-34.2%). Random forest modeling revealed that NTS drove LOC accumulation (explaining 32.95% of the variance) primarily by stimulating Actinobacteria, Ruminococcaceae_UCG-013, Romboutsia, Parasutterella, and Candidatus_Pelagibacter. In contrast, BC maximized TOC (73.51%), LFOC (77.77%), and POC (74.02%) accumulation by significantly boosting the abundances of Bacteroidetes, Leptospirillum, Filimonas, Dyadobacter, and Anaerolinea. This investigation elucidates the mechanistic linkages between microbial taxonomic shifts and specific OC fraction dynamics under varying OMAR and tillage regimes, providing critical insights for optimizing carbon sequestration and sustaining long-term soil fertility in agricultural ecosystems.