DOC, CDOM, FDOM and FTICR data of Arctic tundra soil leaching experiment

Temperature rise in the Arctic is causing deepening of active layers and resulting in the mobilization of deep permafrost dissolved organic matter (DOM). However, the mechanisms of DOM mobilization from Arctic soils, especially upper soil horizons which are drained most frequently through a year, are poorly understood. Here, we conducted a short-term leaching experiment on surface and deep organic active layer soils, from the Yukon River basin, to examine the effects of DOM transport on bulk and molecular characteristics. Our data showed a net release of DOM from surface soils equal to an average of 5% of soil carbon. Conversely, deep soils percolated with surface leachates retained up to 27% of bulk DOM-while releasing fluorescent components (up to 107%), indicating selective release of aromatic components (e.g. lignin, tannin), while retaining non-chromophoric components, as supported by spectrofluorometric and ultra high resolution mass spectroscopic techniques. Our findings highlight the importance of the lateral flux of DOM on ecosystem carbon balance as well as processing of DOM transport through organic active layer soils en route to rivers and streams. This work also suggests the potential role of leachate export as an important mechanism of C losses from Arctic soils, in comparison with the more traditional pathway from soil to atmosphere in a warming Arctic.北极地区的升温正导致冻土活动层（active layer）厚度加深，进而引发深层多年冻土溶解性有机质（dissolved organic matter, DOM）的活化。然而，目前学界对北极土壤尤其是年内排水最为频繁的上层土壤发生层中DOM的活化机制仍知之甚少。本研究针对育空河流域的表层与深层有机活动层土壤开展了短期淋溶实验，以探究DOM运移对土壤整体与分子特征的影响。实验数据显示，表层土壤的DOM净释放量平均相当于土壤碳储量的5%。与之相反，用表层淋溶液渗滤的深层土壤可保留高达27%的总溶解性有机质，同时释放出荧光组分（释放量最高可达107%），这表明土壤选择性释放了芳香族组分（如木质素、单宁）并保留了非生色组分，该结论得到了荧光光谱法与超高分辨质谱技术的佐证。本研究结果凸显了DOM侧向通量对生态系统碳平衡的重要意义，以及DOM在经有机活动层土壤向河流与溪流运移过程中的转化过程。相较于气候变暖背景下北极土壤碳向大气排放的传统途径，本研究还表明淋溶输出可能是北极土壤碳损失的一条重要机制。