【Objective】Mineral-associated organic carbon (MAOC) constitutes the largest and most stable fraction of soil organic carbon (SOC), and increasing its proportion is essential for improving soil quality. Although long-term fertilization has significantly increased the MAOC proportion in SOC in Shajiang black soil, the accumulation patterns of plant- and microbial-derived carbon within MAOC, as well as their relative contributions to SOC, remain unclear. Therefore, this study aims to explore the accumulation characteristics of plant- and microbial-derived carbon and their contribution to MAOC in the 0-20 cm soil depth of Shajiang black soil under long-term fertilization. 【Method】Based on a 34-year field experiment, four treatments were established (no fertilizer and wheat straw return as CK, mineral fertilizer as NPK, mineral fertilizer with half amount of wheat straw return as NPKLS, and mineral fertilizer with full amount of wheat straw return as NPKHS). Biomarkers and chemometric methods were used to investigate the effects of long-term fertilization on plant and microbial-derived carbon in MAOC. 【Results】The results reveal that compared to CK treatment, NPKHS and NPKLS treatments significantly increased the content of MAOC by 29.6% to 54.3% (P < 0.05), with MAOC exhibiting a significant linear positive correlation with SOC (R² = 0.95, P < 0.05) and carbon input (R² = 0.98, P < 0.01). In terms of plant-derived components, the NPKHS treatment induced an increase of 14.8% and 13.3% in the contents of Vanillyl (V) and Syringyl (S) phenols, respectively, while the S/V and C/V ratios decreased by 1.27% to 9.46%. However, the differences in the acid-to-aldehyde ratios (Ad/Al)V and (Ad/Al)S were not significant (P > 0.05). For microbial-derived components, NPKHS treatment significantly elevated the amino sugar content, with an increase of up to 91.4% compared to the control (P < 0.05). Specifically, the contents of fungal residual carbon (FNC) and bacterial residual carbon (BNC) increased by 92.7% and 48.5%, respectively, with fungal necromass dominating (FNC/BNC=4.39). Biomarker analysis indicated that the microbial-derived carbon contribution rate was as high as 72.6% to 73.4%, whereas chemometric methods suggested that the plant-derived carbon contribution ranged from 74.0% to 82.6%. Compared to previous studies on grassland/forest ecosystems (53% to 65%), this proportion appears somewhat unreasonable, suggesting that the chemometric method may have overestimated the contribution from plant sources. 【Conclusion】Our findings indicate that long-term fertilization enhances the accumulation and stability of MAOC in Shajiang black soil primarily by increasing microbial-derived carbon content. This study provides an important reference for the efficient utilization of straw resources and for improving the quality of cultivated land in the Shajiang black soil region.