Different tillage and nitrogen (N) fertilization practices markedly alter soil carbon dynamics, yet the underlying mechanisms and their interactive controls on soil organic matter (OM) biogeochemistry are still not well defined. Soil samples were collected from a 24-year field trial comprising of two tillage practices (conventional and conservation) and two N fertilization rates (low: 12, moderate: 132–172 kg N ha^-1 yr^-1) in Southern Ontario, Canada. Soil organic carbon, molecular-level OM characterization using targeted compound and solid-state ¹³C nuclear magnetic resonance (NMR) analyses, bacterial and fungal abundance using quantitative PCR and community composition using DNA sequencing were used to assess differences in soil carbon processes. Despite similar soil organic carbon concentrations across treatments (16.7–31.2 g/kg), conservation tillage increased specific OM components (i.e., long-chain acyclic lipids, cyclic lipids and simple sugars) than conventional tillage for both N rates. Cutin- and suberin-derived compounds were also higher under conservation than conventional tillage with both N levels, suggesting the preservation of cutin- and suberin-derived compounds with conservation tillage. In contrast, conservation tillage resulted in lower lignin-derived compounds relative to conventional tillage for both N rates (5.4–5.8 vs. 6.3–9.6 mg/g soil OC), likely due to higher decomposition of lignin associated with altered microbial community composition. Under conventional tillage, moderate N fertilization resulted in lower lignin-derived compounds than low N addition (6.3 vs. 9.6 mg/g soil OC). Interestingly, the significant differences between the two N rates for several soil OM compounds and fungal community composition were only observed with conventional tillage but not conservation tillage, suggesting that the control of N fertilization on soil OM dynamics may depend on the type of tillage practices. Overall, tillage management is a more important driver of soil carbon cycling than N fertilization, and conservation tillage may enhance the decomposition of specific soil OM components (i.e., lignin-derived compounds) via changes in microbial communities.

不同的耕作和施氮 (N) 施肥方法显着改变了土壤碳动态，但其对土壤有机质 (OM) 生物地球化学的潜在机制及其交互控制仍未明确定义。土壤样本是从加拿大安大略省南部的一项为期 24 年的田间试验中收集的，该试验包括两种耕作方法（常规和保护）和两种 N 施肥率（低：12，中等：132–172 kg N ha ^-1 yr ^-1 ） . 土壤有机碳，使用目标化合物和固态^{13进行分子级 OM 表征}C 核磁共振 (NMR) 分析、使用定量 PCR 的细菌和真菌丰度和使用 DNA 测序的群落组成被用来评估土壤碳过程的差异。尽管不同处理的土壤有机碳浓度相似（16.7–31.2 g/kg），但在两种氮肥比例下，保护性耕作都比传统耕作增加了特定的有机质成分（即长链无环脂质、环状脂质和单糖）。在保护条件下，角质和木栓质衍生化合物的含量也高于具有两种 N 水平的常规耕作，这表明保护性耕作可以保存角质和木栓质衍生化合物。相比之下，在两种 N 比率（5.4-5.8 对 6.3-9.6 mg/g 土壤 OC）下，与常规耕作相比，保护性耕作导致的木质素衍生化合物较低，可能是由于与改变的微生物群落组成相关的木质素分解程度更高。在常规耕作条件下，适度施氮肥导致木质素衍生化合物低于低施氮量（6.3 对 9.6 毫克/克土壤 OC）。有趣的是，仅在常规耕作而非保护性耕作中观察到几种土壤 OM 化合物和真菌群落组成的两种 N 速率之间的显着差异，这表明 N 施肥对土壤 OM 动态的控制可能取决于耕作方式的类型。总体而言，耕作管理是土壤碳循环的一个比氮肥更重要的驱动因素，保护性耕作可以通过微生物群落的变化促进特定土壤有机质成分（即木质素衍生化合物）的分解。