Abstract: Investigating the variation characteristics of dissolved organic carbon （DOC） in soils of sloping grasslands under different degradation levels is crucial for understanding soil carbon cycling processes. Therefore， this study focuses on severely and moderately degraded sloping grasslands near the forest edge in Hulunbuir City， Inner Mongolia. By measuring the soil DOC content in the surface layer at different slope positions and analyzing the spectral characteristics of dissolved organic matter （DOM）， this study explores the variations of soil DOC across grassland degradation levels. The results showed that grassland degradation significantly reduced soil soil organic carbon （SOC） content， with moderately degraded slope showing 48.97% higher SOC than heavily degraded grassland. However， grassland degradation intensity had no significant effects on DOC content. Heavily degraded slopes showed relatively higher DOC∶SOC ratio and lower stability， which indicated poor soil carbon sequestration. In contrast， the lower slope was relatively stable. Fluorescence spectroscopy revealed that soil dissolved organic matter （DOM） was predominantly derived from plant sources （FI=1.72±0.15， BIX=0.68±0.07）， with minor microbial contributions （HIX=2.15±0.32）， indicating low humification levels. The fluorescence spectral analysis revealed that the soil DOM was predominantly derived from plant sources， with minor microbial contributions， which indicated weak humification. Our findings demonstrate that both degradation intensity and slope position significantly influence SOC stability in sloping grasslands. For restoration of degraded slope grasslands， integrated measures （including reseeding， fertilization， and water conservation measures） are suggested to enhance soil fertility， which are expected to improve soil carbon storage and stability.

Key words: Sloping grassland, Degree of degradation, Slope position, Dissolved organic carbon, UV-fluorescence absorption characteristic

摘要： 研究不同退化程度坡地草地土壤可溶性有机碳（Dissolved organic carbon， DOC）变化特征对土壤碳循环具有重要意义。因此，本研究以内蒙古呼伦贝尔市靠近林缘的重度、中度退化坡地草地（后简称为“坡草地”）为研究对象，通过测定退化坡草地不同坡位土壤DOC含量，结合土壤可溶性有机质（Dissolved organic matter， DOM）的光谱特征，明确不同退化程度坡草地土壤DOC变化。结果表明：草地退化降低了土壤有机碳（Soil organic matter， SOC）含量，中度退化坡草地较重度退化平均提高48.97%，对DOC含量没有产生显著影响。重度退化坡上DOC∶SOC比例较高，稳定性较差，不利于土壤碳固存，而在坡下位置较稳定。结合荧光光谱特征发现，土壤DOM主要属于植物源输入，有少量微生物源有机质输入，腐殖化程度较弱。综上，退化程度和坡位共同影响坡草地土壤有机碳稳定性。对退化坡草地进行修复时，建议采取补播施肥和水保措施提高土壤肥力，增强土壤碳固存。

关键词: 坡地草地, 退化程度, 坡位, 可溶性有机碳, 紫外-荧光吸收特征