To investigate how source and processing control the composition of “terrestrial” dissolved organic matter (DOM), we combine soil and tree leachates, tree DOM, laboratory bioincubations, and ultrahigh resolution Fourier-transform ion cyclotron resonance mass spectrometry in three common landscape types (upland forest, forested wetland, and poor fen) of Southeast Alaska’s temperate rainforest. Tree (Tsuga heterophylla and Picea sitchensis) needles and bark and soil layers from each site were leached, and tree stemflow and throughfall collected to examine DOM sources. Dissolved organic carbon concentrations were as high as 167 mg CL⁻¹ for tree DOM, suggesting tree DOM fluxes may be substantial given the hypermaritime climate of the region. Condensed aromatics contributed as much as 38% relative abundance of spruce and hemlock bark leachates suggesting coniferous trees are potential sources of condensed aromatics to surface waters. Soil leachates showed soil wetness dictates DOM composition and processing, with wetland soils producing more aromatic formulae and allowing the preservation of traditionally biolabile, aliphatic formulae. Biodegradation impacted soil and tree DOM differently, and though the majority of source-specific marker formulae were consumed for all sources, some marker formulae persisted. Tree DOM was highly biolabile (> 50%) and showed compositional convergence where processing homogenized DOM from different tree sources. In contrast, wetland and upland soil leachate DOM composition diverged and processing diversified DOM from different soil sources during bioincubations. Increasing precipitation intensity predicted with climate change in Southeast Alaska will increase tree leaching and soil DOM flushing, tightening linkages between terrestrial sources and DOM export to the coastal ocean.

为了研究来源和加工过程如何控制“陆地”溶解有机物 (DOM) 的组成，我们将土壤和树木渗滤液、树木 DOM、实验室生物孵化和超高分辨率傅里叶变换离子回旋共振质谱仪结合在三种常见景观类型中 (阿拉斯加东南部温带雨林的高地森林、森林湿地和贫瘠的沼泽地。浸出每个地点的树（Tsuga heterophylla和Picea sitchensis）针叶、树皮和土壤层，并收集树干流和穿透量以检查 DOM 来源。溶解的有机碳浓度高达 167 mg CL ^-1对于树 DOM，考虑到该地区的超海洋气候，这表明树 DOM 通量可能很大。浓缩芳烃贡献了高达 38% 的相对丰度的云杉和铁杉树皮渗滤液，这表明针叶树是地表水中浓缩芳烃的潜在来源。土壤渗滤液表明土壤湿度决定了 DOM 的组成和加工过程，湿地土壤产生更多的芳香配方，并允许保存传统上生物不稳定的脂肪配方。生物降解对土壤和树木 DOM 的影响不同，尽管所有来源都消耗了大多数特定来源的标记公式，但一些标记公式仍然存在。树 DOM 具有高度的生物稳定性（> 50%），并且在处理来自不同树源的均质 DOM 时表现出成分收敛。相比之下，湿地和高地土壤渗滤液 DOM 组成分化并在生物孵化期间处理来自不同土壤来源的多样化 DOM。预计随着阿拉斯加东南部气候变化而增加的降水强度将增加树木淋溶和土壤 DOM 冲刷，从而加强陆地来源和 DOM 出口到沿海海洋之间的联系。