Interaction between soil aggregates and humic substances directly determine soil carbon (C) sequestration and stabilization dynamics. This study investigated the influence of different tillage systems on soil humus composition and humic acid (HA) structural characteristics in water stable soil aggregates in the 0−20 and 20−40 cm soil depths. Tillage systems included no-tillage (NTS) and conventional tillage (CTS) both with corn straw returned, and conventional tillage without corn straw returned (CT). Fluorescence, Fourier transform infrared (FTIR) and ¹³C nuclear magnetic resonance (¹³C NMR) spectroscopies were employed to comprehensively characterize soil HA structure in soil aggregate fractions. The results showed that large quantities of humus C was stored in the large macro-aggregates (> 2 mm) and silt/clay (< 0.053 mm) fractions across all tillage systems, highlighting the importance of these aggregate fractions in C sequestration and stabilization. Among all tillage systems, NTS was more conducive in improving humus C content within soil aggregates. The fluorescence and FTIR spectra demonstrated that < 0.053 mm aggregate fractions of all tillage systems were characterized by greater aromatic and phenolic C, and lower carboxyl C groups, indicating complex molecules in HA structures. The> 2 mm aggregates were dominated by aliphatic, methoxyl, hydrophobic and carboxyl C groups, and this result was more evident in NTS indicating improved soil C stability. Comparing all tillage systems, NTS enhanced aliphatic, methoxyl and hydrophobic C in > 2 mm aggregates, which indicate improved soil C stability. The ¹³C NMR results of bulk soil demonstrated that NTS enhanced alkyl, O-alkyl and methoxyl/N-alkyl C in the 0−20 cm. We therefore concluded that NTS is the better system to effectively improve soil C sequestration and stability.

土壤团聚体和腐殖质之间的相互作用直接决定了土壤碳 (C) 封存和稳定动态。本研究调查了不同耕作制度对 0-20 和 20-40 厘米土壤深度的水稳性土壤团聚体中土壤腐殖质组成和腐殖酸 (HA) 结构特征的影响。耕作系统包括免耕 (NTS) 和常规耕作 (CTS)，两者都返回玉米秸秆，以及常规耕作不返回玉米秸秆 (CT)。荧光、傅里叶变换红外 (FTIR) 和¹³ C 核磁共振 ( ¹³C NMR）光谱被用来全面表征土壤团聚体部分的土壤HA结构。结果表明，在所有耕作系统中，大量腐殖质 C 储存在大型宏观聚集体 (> 2 mm) 和淤泥/粘土 (< 0.053 mm) 部分中，突出了这些聚集体部分在 C 封存和稳定中的重要性。在所有耕作系统中，NTS 更有利于提高土壤团聚体中腐殖质 C 的含量。荧光和 FTIR 光谱表明，所有耕作系统的 < 0.053 mm 聚集体部分的特征是芳香族和酚类 C 较多，羧基 C 较低，表明 HA 结构中存在复杂的分子。> 2 mm 的聚集体以脂肪族、甲氧基、疏水和羧基 C 基团为主，这一结果在 NTS 中更为明显，表明土壤碳稳定性得到改善。比较所有耕作系统，NTS 增强了大于 2 毫米团聚体中的脂肪族、甲氧基和疏水性碳，这表明土壤碳稳定性得到改善。这大块土壤的¹³ C NMR 结果表明，NTS 增强了 0-20 cm 范围内的烷基、O-烷基和甲氧基/N-烷基 C。因此，我们得出结论，NTS 是有效改善土壤 C 封存和稳定性的更好系统。