The surface layers of two German grassland soils, a silt loam soil from Dortmund (Soil A) and a sandy loam soil from Hannover (Soil B), were subjected to the Humeomics fractionation to identify the molecular composition of the soil Humeome. The separated Humeomic fractions were analysed by high performance size exclusion chromatography hyphenated to a high-resolution electrospray-Orbitrap Mass Spectrometry (MS). Empirical formulae were obtained by mass data to describe the carbon and nitrogen molecular structures in the soil organic matter (SOM) of both soils. Results showed 175 masses for Soil A and 139 for Soil B distributed among the Humeomic fractions. Masses were classified according to molecular weight, unsaturation degree, oxygenation, and presence of nitrogen in the formula. The molecular information obtained with MS was consistent with the physical–chemical properties and environmental condition of the two grassland soils: (i) nitrogenated compounds were generally more numerous and more relatively abundant in the Humeome of Soil B, which was more anoxic and lower in C/N ratio than Soil A, (ii) highly oxygenated compounds were more numerous and abundant in the more oxic Soil A, (iii) most unsaturated formulae were comparatively more abundant in Soil A than Soil B, in line with differences in environmental conditions. The empirical formulae were then matched with their molecular structures, based on the application of ChemSpider and PubChem databases, and were found to be distributed into 16 specific chemical groups. The Van Krevelen plots built on the resulting carbon and nitrogen molecular structures provided a visual comparison of the Humeome of the two soils. The organosoluble fractions in both soils were dominated by aliphatic amides and saccharide ethers, while the hydrosoluble fractions comprised mainly aromatic amides, heterocyclic nitrogen compounds, and saccharide ethers. Even though the two soils contained different compounds, 66 molecules were found to be common. Based only on differences in soil texture and oxic conditions, these findings indicate the existence of similar molecular dynamics in the stabilization of organic matter in these two grassland soils. The main common group in the Humeome of both soils was the saccharide ethers, which were additionally bound to aromatic compounds in the hydrosoluble fractions. Our detailed molecular study of the Humeome of these grassland soils confirms the potential of the Humeomic procedure to assess not only the carbon and nitrogen molecular composition in SOM, but also the mechanism of their long-term persistence.

中文翻译：

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两种不同草地土壤休ome中碳和氮分子的结构表征

对两种德国草地土壤（多特蒙德的粉壤土（土壤A）和汉诺威的沙质壤土（土壤B）的表层进行了Humeomics分级分离，以鉴定土壤休ome组的分子组成。分离的腐殖质馏分通过连接至高分辨率电喷雾Orbitrap质谱（MS）的高效尺寸排阻色谱法进行分析。通过质量数据获得了经验公式，以描述两种土壤的有机质（SOM）中的碳和氮分子结构。结果表明，土壤A的质量为175，土壤B的质量为139。根据分子式中的分子量，不饱和度，氧合和氮的存在将质量分类。MS获得的分子信息与两种草原土壤的物理化学性质和环境条件一致：（i）土壤B的Humeome中的含氮化合物通常较多且相对丰富，而B的Humeome较缺氧且较低。 C / N比值比土壤A大，（ii）高氧土壤A中的高氧化化合物数量更多且丰富，（iii）土壤A中大多数不饱和分子比土壤B相对丰富，这要符合环境条件的差异。然后，根据ChemSpider和PubChem数据库的应用，将经验公式与其分子结构进行匹配，并发现它们可分为16个特定的化学基团。基于所得碳和氮分子结构的Van Krevelen图提供了两种土壤的Humeome的直观比较。两种土壤中的有机可溶级分均以脂族酰胺和糖醚为主，而水溶性级分主要包括芳族酰胺，杂环氮化合物和糖醚。即使两种土壤包含不同的化合物，也发现共有66个分子。仅基于土壤质地和含氧条件的差异，这些发现表明这两种草原土壤在稳定有机质方面存在相似的分子动力学。两种土壤的腐殖质中最主要的共同基团是糖醚，它们在水溶性部分中还与芳族化合物结合。