Photooxidation of dissolved organic sulfur (DOS) in soils and natural waters plays an important role in the sulfur biogeochemical cycle. However, the structural-dependent photoliabilities of DOS from different sources remain unclear. Here, the molecular structures and photooxidation behaviors of DOS in pyrogenic dissolved black matter (PyDOM) derived from rice straw-pyrolyzed biochar (referred to as PyDOM-S and considered to be representative of black carbon from prairie fires) were thoroughly characterized and compared with those of DOS in leached dissolved organic matter (LDOM) derived from aerobically decomposed rice straw (referred to as LDOM-S and considered to be generally representative of organic-rich horizons in soils and peats). The Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis revealed that both PyDOM-S and LDOM-S were, respectively, dominated by aliphatic (60.4 % and 41.1 %) and lignin-like compounds (35.1 % and 40.1 %), followed by minimal aromatic and polyaromatic compounds (2.8 % and 11.9 % in total). As demonstrated by the sulfur K-edge X-ray absorption near-edge structure (S-XANES) analysis, PyDOM-S consisted mainly of organosulfate (80.4 %) contrasting to the diversified and mingled reduced sulfurs (62.7 %) and oxidized sulfurs (37.3 %) of LDOM-S. Under simulated sunlight irradiation, 74 % of sulfur in PyDOM-S was photomineralized to sulfate within 24 h and totaling 89 % after 168 h, but only 9 % and 42 % for LDOM-S given the same periods of time, confirming the much faster photomineralization of PyDOM-S. After 168-h irradiation, almost all molecules in PyDOM-S disappeared, whereas a large proportion (44.2 %) of LDOM-S molecules (mainly aliphatic and lignin-like compounds) were photo-resistant. Furthermore, the photomineralization of PyDOM-S was mainly contributed by the final and complete oxidation of organosulfate to sulfate; however, the photooxidation of LDOM-S was dominated by the sequential oxidation of exocyclic sulfur and heterocyclic sulfur to organosulfate prior to releasing sulfate. These results highlight that pyrogenic-sourced PyDOM-S and diagenesis-derived LDOM-S exhibit contrasting photooxidation behaviors due to the associated distinct molecular structures.

中文翻译：

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稻草生物炭释放的溶解有机硫与好氧分解稻草释放的分子结构和光氧化行为的对比


土壤和天然水中溶解有机硫 （DOS） 的光氧化在硫的生物地球化学循环中起着重要作用。然而，来自不同来源的 DOS 的结构依赖性光易感性仍不清楚。在这里，彻底表征了水稻秸秆热解生物炭（简称 PyDOM-S，被认为代表草原火灾中的黑碳）衍生的热原溶解黑物质 （PyDOM） 中 DOS 的分子结构和光氧化行为，并与好氧分解稻草衍生的浸出溶解有机物 （LDOM） 中的 DOS 的分子结构和光氧化行为进行了比较（称为 LDOM-S，被认为通常代表富含有机物的层位土壤和泥炭）。傅里叶变换离子回旋共振质谱 （FT-ICR MS） 分析显示，PyDOM-S 和 LDOM-S 分别以脂肪族化合物 （60.4 % 和 41.1 %） 和木质素类化合物 （35.1 % 和 40.1 %） 为主，其次是最低限度的芳香族和多芳香族化合物 （共 2.8 % 和 11.9 %）。硫 K 边缘 X 射线吸收近边缘结构 （S-XANES） 分析表明，PyDOM-S 主要由有机硫酸盐 （80.4%） 组成，而 LDOM-S 的多样化和混合还原硫 （62.7%） 和氧化硫 （37.3%） 形成鲜明对比。在模拟阳光照射下，PyDOM-S 中 74% 的硫在 24 小时内光矿化为硫酸盐，168 小时后总计 89%，但在相同时间内，LDOM-S 仅为 9% 和 42%，证实了 PyDOM-S 的光矿化速度要快得多。照射 168 小时后，PyDOM-S 中几乎所有分子都消失了，而很大一部分 （44.2%） 的 LDOM-S 分子 （主要是脂肪族和木质素样化合物） 具有光抗性。 此外，PyDOM-S 的光矿化主要由有机硫酸盐最终完全氧化为硫酸盐贡献;然而，LDOM-S 的光氧化主要是在释放硫酸盐之前，外环硫和杂环硫依次氧化成有机硫酸盐。这些结果强调，由于相关不同的分子结构，热原来源的 PyDOM-S 和成岩衍生的 LDOM-S 表现出截然不同的光氧化行为。