Molecular dissolved organic matter composition in lakes across Sweden as relative intensities of FT-ICR-MS peaks and PARAFAC components and optical indices@en

Whether intrinsic molecular properties or extrinsic factors such as environmental conditions control the decomposition of natural organic matter across soil, marine and freshwater systems has been subject to debate. Comprehensive evaluations of the controls that molecular structure exerts on organic matter's persistence in the environment have been precluded by organic matter's extreme complexity. Here we examine dissolved organic matter from 109 Swedish lakes using ultrahigh-resolution mass spectrometry and optical spectroscopy to investigate the constraints on its persistence in the environment. We find that degradation processes preferentially remove oxidized, aromatic compounds, whereas reduced, aliphatic and N-containing compounds are either resistant to degradation or tightly cycled and thus persist in aquatic systems. The patterns we observe for individual molecules are consistent with our measurements of emergent bulk characteristics of organic matter at wide geographic and temporal scales, as reflected by optical properties. We conclude that intrinsic molecular properties are an important control of overall organic matter reactivity.在土壤、海洋与淡水生态系统中，究竟是分子固有属性还是环境条件等外在因素调控着天然有机物（natural organic matter, NOM）的降解过程，这一问题长期以来备受学界争议。由于天然有机物本身具有极强的复杂性，学界此前难以全面评估分子结构对其环境持久性的调控作用。本研究针对瑞典109个湖泊中的溶解态有机物（dissolved organic matter, DOM）展开分析，采用超高分辨质谱（ultrahigh-resolution mass spectrometry, UHR-MS）与光学光谱法，探究其环境持久性的制约因素。研究发现，降解过程会优先去除氧化态芳香族化合物（aromatic compounds），而还原态脂肪族化合物（aliphatic compounds）及含氮化合物要么具备抗降解能力，要么处于紧密循环状态，因此能够在水生生态系统中留存。我们在单个分子层面观测到的变化规律，与光学特性所反映的、在广泛地理与时间尺度上测得的有机物整体涌现特征的测量结果一致。综上，分子固有属性是调控整体有机物反应活性的重要因素。