Global environmental change is altering the quality and quantity of plant inputs into soil. However, it is unclear how these long-term changes may fundamentally shift the biogeochemistry of soil carbon in forests. To better understand how varied detrital inputs alter soil organic matter (OM) biogeochemistry and composition at the molecular-level, soil samples were collected from a 20 year detrital manipulation experiment in an old-growth coniferous rainforest in Western Oregon. The experiment includes ambient (control) plots and six treatments: Double Litter, Double Wood, No Roots, No Litter, No Inputs and OA-less (replacement of O and A horizons with B horizon). Total soil carbon and nitrogen, molecular-level OM composition using solid-state ¹³C nuclear magnetic resonance, and targeted compound extractions were measured. Although soil carbon did not increase with Double Litter and Double Wood, microbial biomass and the decomposition of specific forms of soil OM (i.e., cellulose) increased, likely due to sustained soil priming over 20 years. Mineral (0–10 cm) soil carbon was similar across litter exclusion treatments (No Litter, No Roots, No Inputs), however, soil OM decomposition increased relative to the control. Microbial-derived lipids increased under Double Litter but decreased when above-ground litter was excluded. Notably, needle-derived lipids decreased with above-ground litter exclusion and root-derived compounds did not change under below-ground root exclusion. These results suggested that above-ground litter alters soil carbon biogeochemistry in surface soils to a greater extent than below-ground inputs. This study also demonstrated that long-term soil carbon biogeochemical trajectories were mostly governed by litter quality, quality and microbial processing of above-ground inputs.

全球环境变化正在改变植物投入土壤的质量和数量。然而，尚不清楚这些长期变化如何从根本上改变森林中土壤碳的生物地球化学。为了更好地了解不同的碎屑输入如何在分子水平上改变土壤有机质 (OM) 生物地球化学和组成，在俄勒冈州西部的一个古老针叶雨林中进行了 20 年的碎屑操作实验，收集了土壤样本。该实验包括环境（对照）地块和六种处理：双胎、双木、无根、无胎、无输入和无 OA（用 B 水平替换 O 和 A 水平）。土壤总碳和氮，使用固态^{13的分子水平 OM 组成}测量了 C核磁共振和目标化合物提取物。虽然土壤碳没有随着 Double Litter 和 Double Wood 增加，但微生物生物量和特定形式的土壤 OM（即纤维素）的分解增加了，这可能是由于 20 年以上的持续土壤引发。矿物（0-10 cm）土壤碳在凋落物排除处理（无凋落物、无根、无输入）中相似，但是，相对于对照，土壤 OM 分解增加。微生物来源的脂质在双窝下增加，但在排除地上垃圾时减少。值得注意的是，针衍生的脂质随着地上枯落物的排除而减少，而根衍生的化合物在地下根排除的情况下没有变化。这些结果表明，与地下输入相比，地上凋落物对表层土壤中土壤碳生物地球化学的影响更大。该研究还表明，长期土壤碳生物地球化学轨迹主要受凋落物质量、地上输入的质量和微生物处理的影响。