Conservation agriculture such as conservation tillage and crop rotation can alter soil organic matter (OM) storage and cycling. However, little is known about how these methods alter the molecular-level soil OM composition and turnover. We collected soil samples (0−10 cm) from a 37-year experiment with contrasting diversity crop rotations under conventional tillage and conservation tillage. Soil organic carbon concentrations, molecular-level OM composition and microbial biomass and community structure were measured. Soil organic carbon concentrations were similar between the two tillage practices, likely due to the balance between carbon loss via degradation and carbon gains through incorporation of crop residues in soil. We observed significant changes in soil OM composition between conventional tillage and conservation tillage despite similar soil organic carbon concentrations. Under long-term conservation tillage practice, lower suberin-derived compounds and higher lignin-derived compounds were observed. The degradation of cutin-, lignin-derived compounds and soil OM were lower under conservation tillage among most rotations. The changes in lignin-derived compounds and degradation were microbially driven and likely controlled by substrate utilization. In contrast, the differences in suberin-derived compounds were likely associated with crop residue-induced OM inputs and/or the differential introduction of OM (e.g. root materials) to the upper layer of soil due to conventional tillage vs. conservation tillage managements. These findings reveal that microbial degradation, OM inputs from crop residues and management-induced OM distribution in soil layers may alter agricultural soil OM composition. Additionally, we found that the differences in some specific groups of compounds between conventional tillage and conservation tillage were lower in crop rotations with higher diversity, highlighting the benefits of the interaction between diverse rotations and conservation tillage.

保护性耕作和作物轮作等保护性农业可以改变土壤有机质的存储和循环。但是，对于这些方法如何改变分子水平的土壤OM组成和周转率知之甚少。我们收集了一项为期37年的实验的土壤样品（0-10厘米），对比了传统耕作和保护性耕作下作物轮作的多样性。测量了土壤有机碳浓度，分子水平的OM组成以及微生物生物量和群落结构。两种耕作方式之间的土壤有机碳浓度相似，这可能是由于降解造成的碳损失与作物残渣掺入土壤获得的碳增加之间的平衡。尽管土壤有机碳含量相似，我们仍观察到常规耕作和保护性耕作之间土壤有机质组成发生了显着变化。在长期的保护性耕作实践中，观察到了较低的木脂蛋白来源的化合物和较高的木素来源化合物。在大多数耕作中，在保护性耕作下角质，木质素衍生的化合物和土壤有机质的降解率较低。木质素衍生化合物的变化和降解是微生物驱动的，并且很可能由底物利用率控制。相反，由于传统的耕作与保护性耕作管理方式不同，源自地物的化合物的差异可能与农作物残渣诱导的有机质输入和/或有机质（例如根系物质）向土壤上层的差异引入有关。这些发现表明，微生物降解，农作物残留的有机物输入以及管理引起的土壤层中有机物分布可能会改变农业土壤的有机物成分。此外，我们发现，常规耕作和保护性耕作之间某些特定种类化合物的差异在轮作中具有较低的多样性，多样性更高，这突出表明了不同轮作和保护性耕作之间相互作用的好处。