Litter decomposition produces labile and recalcitrant forms of dissolved organic matter (DOM) that significantly affect soil carbon (C) sequestration. Chemical analysis of this DOM can provide important knowledge for understanding soil DOM dynamics, but detailed molecular analyses on litter derived DOM are scarce. Here we use ultrahigh resolution mass spectrometry (FT-ICR MS) to characterize the molecular composition of DOM from fresh and progressively decomposed litter samples. We compared high reactive (HR) and low reactive (LR) litter sources with regard to changes in the chemistry and bioavailability of leachates throughout the early phase of litter decay. We show that litter reactivity is a driver of chemical changes in the leached DOM of litter species. Birch, alder and Vaccinium (i.e. HR) litter initially produced more DOM with a higher lability than that of spruce, pine and wood (i.e. LR) litter. Labile oxidized phenolic compounds were abundant in leachates produced during the initial HR litter decay stages, indicating litter lignin degradation. However, the similarity in chemistry between HR and LR leachates increased during the litter decay process as highly leachable structures in HR litter were depleted. In contrast, chemistry of leachates from LR litter changed little during the litter decay process. The oxygenated phenolic compounds from HR litter were driving the lability of HR leachates and the changes in relative abundance of molecules during DOM incubation. This appeared to result in the creation of stable aliphatic secondary microbial compounds. In LR leachates, lability was driven by labile aliphatic compounds, while more resistant phenolic compounds were associated with recalcitrance. These results show how DOM dynamics follow different paths depending on litter reactivity, which has important implications for soil biogeochemistry and C sequestration.

凋落物分解会产生不稳定的顽固形式的溶解有机物（DOM），这会严重影响土壤碳（C）的固存。该DOM的化学分析可以为理解土壤DOM动力学提供重要的知识，但是对枯枝落叶DOM的详细分子分析却很少。在这里，我们使用超高分辨率质谱（FT-ICR MS）来表征新鲜和逐步分解的垃圾样品中DOM的分子组成。我们比较了高反应性（HR）和低反应性（LR）的凋落物来源，研究了整个凋落物腐烂早期渗滤液的化学性质和生物利用度的变化。我们显示，垃圾的反应性是垃圾种类中浸出DOM中化学变化的驱动力。桦木，al木和牛痘（例如HR）垃圾最初比云杉，松木和木材（例如LR）垃圾产生更多的DOM，并且具有更高的不稳定性。在最初的HR凋落物腐烂阶段产生的渗滤液中，不稳定的氧化酚类化合物含量很高，表明凋落物木质素降解。但是，由于凋落物中高度可浸出的结构被耗尽，HR和LR浸出物在化学上的相似性在凋落物腐烂过程中增加了。相比之下，LR凋落物的渗滤液的化学性质在凋落物腐烂过程中变化不大。来自HR凋落物的含氧酚类化合物正在驱动HR浸出液的不稳定性以及DOM孵育过程中分子相对丰度的变化。这似乎导致产生稳定的脂族第二微生物化合物。在LR渗滤液中，不稳定是由不稳定的脂族化合物驱动的，而更具抗性的酚类化合物与顽固性有关。这些结果表明，DOM动力学如何取决于凋落物的反应性，这对土壤生物地球化学和碳固存具有重要意义。