Understanding the chemical composition, origin, and molecular structure of dissolved organic matter (DOM) in multi-interface runoff is essential for comprehending the fate of laterally transported DOM in complex soil-epikarst systems of karst hillslopes. Limited information, however, is available for the optical properties and molecular compositions of the transported OM in multiple runoff components on the karst hillslope in relation to land-uses and soil thicknesses. In this study, we conducted a study to observe the changes in the quantity and quality of DOM in multiple interface flow (surface, subsurface, and epikarst) during natural rainfall events in 2022 in karst hillslopes that are covered by different land uses (cropland and shrubland) and soil thicknesses (with mean depths of 66.0 cm for deeper soil and 35.4 cm for shallower soil) in the karst region of southwest China. chemcial compositions of runoff DOM were determined by optical analysis and microbial compositions in runoff were inferred with high-throughput sequencing. The results showed that the soil-epikarst structure was controlling the runoff DOM quantity and quality during rainfall events. A decrease in the aromaticity, humification, unsaturation, and oxidation degree and an increase in carbohydrate, aminosugars, protein, and lipid compounds were found from surface to epikarst flow, indicating that plant-and soil-derived carbon decreased, while the microbially-derived carbon increased. The results were further comfirmed by the higher bacterial richness and diversity, along with fungal diversity in the epikarst flow compared to other runoff components. The bio-labile protein materials (C2) were the most important component of runoff DOM output in karst hillslopes. In surface and subsurface flow, rainfall amount, runoff rate, and discharge significantly affected the DOM concentration and quality during rainfalls, indicating that the dynamics of DOM in runoff from karst hillslopes were predominantly influenced by hydrological processes. Furthermore, the runoff DOM quality in cropland was dominated by lower unsaturation and oxidation degrees and higher protein component, compared to those in shrubland. The compositions of DOM in runoff from hillslope plots with thicker soils were primarily characterized by microbially-derived materials. Our findings were conducive to understanding the mechanism governing the migration of DOM quality and quantity in discharge during multi-interface hydrological processes on karst hillslopes.

中文翻译：

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岩溶山坡降雨过程中多种径流成分中溶解有机物的光学性质和分子组成

了解多界面径流中溶解有机物 (DOM) 的化学成分、来源和分子结构对于理解喀斯特山坡复杂土壤-表岩系统中 DOM 横向迁移的命运至关重要。然而，关于喀斯特山坡上多个径流成分中输送的 OM 的光学特性和分子组成与土地利用和土壤厚度的关系，可获得的信息有限。在本研究中，我们对不同土地利用（农田和地表）覆盖的岩溶山坡进行了2022年自然降雨事件中多界面流（地表、地下和表层岩溶）中DOM数量和质量变化的研究。西南喀斯特地区的灌木丛）和土壤厚度（深层土壤平均深度为 66.0 厘米，浅层土壤平均深度为 35.4 厘米）。通过光学分析确定径流 DOM 的化学成分，并通过高通量测序推断径流中的微生物组成。结果表明，土壤表层岩溶结构控制着降雨过程中径流 DOM 的数量和质量。从地表到表层岩溶流，发现芳香度、腐殖化度、不饱和度和氧化度降低，碳水化合物、氨基糖、蛋白质和脂质化合物增加，表明植物和土壤来源的碳减少，而微生物来源的碳减少。碳增加。与其他径流成分相比，表层岩溶流中更高的细菌丰富度和多样性以及真菌多样性进一步证实了结果。生物不稳定蛋白质物质（C2）是喀斯特山坡径流DOM输出的最重要组成部分。在地表和地下径流中，降雨量、径流量和流量对降雨期间的DOM浓度和质量有显着影响，表明岩溶山坡径流中DOM的动态主要受水文过程的影响。此外，与灌丛相比，农田径流 DOM 质量主要由较低的不饱和度和氧化度以及较高的蛋白质成分决定。土壤较厚的山坡地块径流中的 DOM 成分主要由微生物来源的物质表征。我们的研究结果有助于理解岩溶山坡多界面水文过程中排放的DOM质量和数量的迁移机制。