Dissolved organic matter composition and structural fingerprints from a set of four marine and one freshwater environments@en

Natural dissolved organic matter (DOM) comprises a broad range of dissolved organic molecules in aquatic systems and is among the most complex molecular mixtures known. Here we show, by comparing detailed structural fingerprints of individual molecular formulae in DOM from a set of four marine and one freshwater environments, that a major component of DOM is molecularly indistinguishable in these diverse samples. Molecular conformity was not only apparent by the co-occurrence of thousands of identical molecular formulae, but also by identical structural features of those isomers that collectively represent a molecular formula. The presence of a large pool of compounds with identical structural features in DOM is likely the result of a cascade of degradation processes or common synthetic pathways that ultimately lead to the formation of a universal background, regardless of origin and history of the organic material. This novel insight impacts our understanding of long-term turnover of DOM as the underlying mechanisms are possibly universal.

天然溶解有机质（dissolved organic matter, DOM）指水生系统中种类繁杂的溶解有机分子集合，是目前已知最为复杂的分子混合物之一。本研究通过对比四种海洋与一种淡水环境来源的DOM中单个分子式的精细结构指纹，发现不同环境样品中的DOM主要组分在分子层面无法区分。这种分子一致性不仅体现在数千个相同分子式的共同出现，还体现在对应同一分子式的所有同分异构体所共有的相同结构特征上。DOM中存在大量具有相同结构特征的化合物，这一现象大概率源于一系列级联降解过程或共同的合成路径：无论有机质的来源与演化历史如何，这些过程最终都会形成一个通用的背景组分。这一全新认知革新了我们对DOM长期周转过程的理解，因为其背后的作用机制可能具有普适性。