Soil organic matter (SOM) controls various soil properties and functions, possibly at molecular composition level. Better understanding of the SOM chemistry is vital for evaluating soil quality and the effectiveness of soil restoration practices. This study aimed to characterize the dynamic changes of SOM chemistry during the restoration process from a severely degraded Mollisol (MO) under short-term natural and agricultural management practices. It further facilitated to investigate the influencing factors of such changes, as well as helped to unveil the possible origins of SOM that control the carbon sequestration and stabilization. A field restoration experiment based on the parent material (PM) of MO was established in 2004. The restoration experiment included two no-tilled soils supporting natural fallow (NatF) and alfalfa (Alfa) and three arable soils: without chemical fertilizer and organic inputs (F0C0), with chemical fertilization and part (F1C1), or all (F1C2) aboveground biomass inputs. The surface soils (0–20 cm) after 2 and 8 years of different restoration practices were collected to investigate the molecular compositions of SOM by ¹³C cross-polarization/total sideband suppression solid-state nuclear magnetic resonance (CP/TOSS NMR) and CP/TOSS with dipolar dephasing techniques. Two reference soils including surface MO and PM were also determined. Compared with PM, the proportions of O-alkyl and alkyl C groups increased by 5.8–16.0% and 2.8–5.0% after 8-year soil restoration, respectively, while proportions of nonpolar alkyl C, aromatic C, and carbonyl/amide C groups decreased by 5.0–24.1%, 17.3–55.0%, and 10.1–23.2%, respectively. Larger changes were mainly found in F1C2. Redundant analysis showed that the chemical structure of SOM varied largely among treatments after 2-year soil restoration, but the variations became smaller after 8-year soil restoration, with the SOM chemistry in F1C2 being more closed to MO. The variations were mainly driven by protonated O-alkyl C, anomeric C, and OCH₃ C; unprotonated aromatic C; and amid C via axis 1 and nonpolar alkyl C, protonated aromatic C, and unprotonated anomeric C via axis 2. The contents of soil organic carbon and amino sugars correlated positively with protonated O-alkyl C and aromatic C groups, suggesting soil microbial residues related to the changes of SOM chemistry. Natural perennials and agricultural restoration practices altered the SOM chemistry by adding different quality and quantity of plant residues during the soil restoration from a severely degraded Mollisol. Plant-derived organic carbon was transformed into SOM, and higher organic inputs could further facilitate the restoration of SOM chemistry. These organic components, together with soil microbial residues, contributed to the restoration of SOM chemistry and subsequently influenced the SOM stabilization.

土壤有机质 (SOM) 可能在分子组成水平上控制各种土壤特性和功能。更好地了解 SOM 化学对于评估土壤质量和土壤恢复实践的有效性至关重要。本研究旨在表征在短期自然和农业管理实践下严重退化的 Mollisol (MO) 恢复过程中 SOM 化学的动态变化。它进一步促进了研究这些变化的影响因素，并有助于揭示控制碳封存和稳定的 SOM 的可能起源。2004年建立了基于MO母材（PM）的田间恢复试验。恢复试验包括两种支持自然休耕（NatF）和苜蓿（Alfa）的免耕土壤和三种耕地：不施化肥和有机投入（F0C0），施化肥和部分（F1C1），或全部（F1C2）地上生物质投入。收集经过 2 年和 8 年不同恢复实践的表层土壤（0-20 厘米），通过以下方法研究 SOM 的分子组成¹³C 交叉极化/总边带抑制固态核磁共振 (CP/TOSS NMR) 和具有偶极去相技术的 CP/TOSS。还测定了两种参考土壤，包括表面 MO 和 PM。与PM相比，土壤恢复8年后，O-烷基和烷基C基团的比例分别增加了5.8-16.0%和2.8-5.0%，而非极性烷基C、芳香C和羰基/酰胺C基团的比例分别下降了 5.0-24.1%、17.3-55.0% 和 10.1-23.2%。较大的变化主要出现在 F1C2 中。冗余分析表明，土壤修复 2 年后 SOM 的化学结构在不同处理间变化较大，但土壤修复 8 年后变化变小，F1C2 中的 SOM 化学更接近 MO。变化主要由质子化的 O-烷基 C 驱动，₃C; 未质子化的芳香族 C；和在 C 通过轴 1 和非极性烷基 C、质子化芳香 C 和非质子化异头 C 通过轴 2。土壤有机碳和氨基糖的含量与质子化的 O-烷基 C 和芳香 C 基团呈正相关，表明土壤微生物残留相关SOM 化学的变化。天然多年生植物和农业恢复实践通过在严重退化的 Mollisol 的土壤恢复过程中添加不同质量和数量的植物残留物来改变 SOM 化学。植物来源的有机碳转化为 SOM，更高的有机投入可以进一步促进 SOM 化学的恢复。这些有机成分与土壤微生物残留物一起促进了 SOM 化学的恢复，并随后影响了 SOM 的稳定性。