Soil organic carbon fractions may vary with soil development and soil genesis controls its vertical distribution. The objectives of this study were to determine organic carbon fractions in soil derived from loess parent material and the role of relief in its vertical distribution. Five soil pedons, i.e., Typic Ustorthents (Rajar), Typic Calciustepts (Missa), Udic Calciustepts (Basal), Udic Haplustalfs (Guliana), and Typic Hapludalfs (Mansehra), were selected along a loess toposequence and sampled at genetic horizon level. Soils were characterized for texture, pH, calcium carbonate (CaCO 3 ), and organic carbon fractions including total organic carbon (TOC), dissolved organic carbon (DOC), particulate organic carbon (POC), HCl-insoluble organic carbon, and density fractions, i.e., heavy fraction (HF) and light fraction (LF). Total organic carbon content ranged from 0.03 to 0.98% in these soils and significantly differed with soil depth within each soil and soil type. Mansehra and Guliana had 0.04 and 0.031% POC, respectively, which was greater compared to remaining soils. Dissolved organic carbon was greater in the Basal followed by Mansehra, Rajar, Missa, and Guliana soil profiles, and distribution remains uniform throughout the profile’s depth. Insoluble C fraction was 0.214% in Mansehra profiles followed by 0.156% in Rajar, 0.078% in Basal, 0.063% in Guliana, and 0.091% in Missa soil profiles. The Mansehra soil profiles had the highest (0.008 and 0.30%) content of both light and heavy fractions. Total organic carbon had little correlation with clay. Particulate organic carbon, DOC, and HCl-insoluble organic carbon had a significant correlation with TOC. The HF had the strongest correlation with TOC, while LF had a negative correlation. The soil organic fractions significantly differed with soil type and soil genesis. The soils at gentle slopes are dominant in most of the organic carbon fractions due to higher development stage.

中文翻译：

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黄土表层土壤有机碳组分的变化

土壤有机碳含量可能随土壤发育而变化，土壤发生控制其垂直分布。本研究的目的是确定源自黄土母质的土壤中的有机碳含量以及浮雕在其垂直分布中的作用。沿着黄土地形序列选择了五种土壤土壤，即 Typic Ustorthents (Rajar)、Typic Calciustepts (Missa)、Udic Calciustepts (Basal)、Udic Haplustalfs (Guliana) 和 Typic Hapludalfs (Mansehra)，并在遗传层级进行采样。对土壤的质地、pH、碳酸钙 (CaCO 3 ) 和有机碳组分进行表征，包括总有机碳 (TOC)、溶解有机碳 (DOC)、颗粒有机碳 (POC)、HCl 不溶性有机碳和密度组分，即重馏分（HF）和轻馏分（LF）。这些土壤中的总有机碳含量在 0.03% 到 0.98% 之间，并且在每种土壤和土壤类型中随土壤深度的不同而显着不同。Mansehra 和 Guliana 的 POC 分别为 0.04% 和 0.031%，与剩余土壤相比更高。基底层的溶解有机碳较多，其次是 Mansehra、Rajar、Missa 和 Guliana 土壤剖面，并且在剖面的整个深度分布保持均匀。Mansehra 剖面中的不溶 C 分数为 0.214%，其次是 Rajar 的 0.156%、Basal 的 0.078%、Guliana 的 0.063% 和 Missa 土壤剖面的 0.091%。Mansehra 土壤剖面的轻质和重质组分含量最高（0.008 和 0.30%）。总有机碳与粘土几乎没有相关性。颗粒有机碳、DOC 和 HCl 不溶性有机碳与 TOC 有显着相关性。HF 与 TOC 的相关性最强，而 LF 与 TOC 呈负相关。土壤有机成分随土壤类型和土壤成因显着不同。由于发育阶段较高，缓坡土壤在大部分有机碳组分中占优势。