Decomposing foliar litter organic matter (LOM) in forested watersheds is an essential terrestrial source of dissolved organic matter (DOM) to aquatic ecosystems. To evaluate the relationship of chemical composition between LOM and DOM, we collected freshly fallen leaves of white oak (Quercus alba) and conducted an 80-week field decomposition experiment along a small elevation gradient in a floodplain within the Congaree National Park, South Carolina. Foliar litters were collected for water extraction and instrumental analyses using pyrolysis GC/MS, UV/VIS and fluorescence spectrophotometry. Factor analyses of pyrolysates showed that fresh LOM was mainly composed of lignin compounds (LgC), phenolic compounds (PhC), and carbohydrate (Carb), and the change in composition was relatively small throughout the decomposition process. In contrast, there were two distinct chemical compositions of DOM in early (between 0–8 weeks) and late phases (between 16–80 weeks). The early phase had a higher percentage of PhC, but the late phase contained higher percentages of Carb, unsaturated hydrocarbon (UnSaH), aromatic hydrocarbon (ArH), and nitrogen-containing compounds (Ntg). The fluorescence emission-excitation matrix showed there was an increasing trend in humic and fulvic-like fractions in DOM over time, matching well with increases of UnSaH and ArH fractions from the results of pyrolysis GC/MS. Our study illustrated that the changes of chemical components in LOM and water extractable DOM were not parallel during the decomposition process and the degradation of lignin and phenolic compounds was one of the controlling factors on the production of DOM.

中文翻译：

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分解过程中树叶凋落物和溶解有机物的分子动力学

森林流域中分解的凋落物有机质 (LOM) 是水生生态系统溶解有机质 (DOM) 的重要陆地来源。为了评估 LOM 和 DOM 之间化学成分的关系，我们收集了白橡树 (Quercus alba) 的新鲜落叶，并在南卡罗来纳州康加里国家公园内的洪泛区沿小海拔梯度进行了为期 80 周的田间分解实验。收集落叶用于水提取和使用热解 GC/MS、UV/VIS 和荧光分光光度法的仪器分析。热解产物的因子分析表明，新鲜的 LOM 主要由木质素化合物 (LgC)、酚类化合物 (PhC) 和碳水化合物 (Carb) 组成，并且在整个分解过程中组成的变化相对较小。相比之下，DOM 在早期（0-8 周之间）和晚期（16-80 周之间）有两种不同的化学成分。早期阶段具有较高百分比的 PhC，但晚期阶段包含较高百分比的 Carb、不饱和烃 (UnSaH)、芳香烃 (ArH) 和含氮化合物 (Ntg)。荧光发射激发矩阵显示 DOM 中腐殖质和类黄腐酸组分随时间增加的趋势，与热解 GC/MS 结果显示的 UnSaH 和 ArH 组分的增加非常吻合。我们的研究表明，分解过程中 LOM 和水可提取 DOM 中化学成分的变化并不平行，木质素和酚类化合物的降解是 DOM 产生的控制因素之一。