Dissolved organic carbon (DOC) from Oa horizons has been proposed to be an important contributor for subsoil organic carbon stocks. We investigated the fate of DOC by directly injecting a DOC solution from 13C labelled litter into three soil depths at beech forest sites. Fate of injected DOC was quantified with deep drilling soil cores down to 2 m depth, 3 and 17 months after the injection. 27 ± 26% of the injected DOC was retained after 3 months and 17 ± 22% after 17 months. Retained DOC was to 70% found in the first 10 cm below the injection depth and on average higher in the topsoil than in the subsoil. After 17 months DOC in the topsoil was largely lost (− 19%) while DOC in the subsoil did not change much (− 4.4%). Data indicated a high stabilisation of injected DOC in the subsoils with no differences between the sites. Potential mineralisation as revealed by incubation experiments however, was not different between DOC injected in topsoil or subsoils underlining the importance of environmental factors in the subsoil for DOC stabilisation compared to topsoil. We conclude that stability of DOC in subsoil is primary driven by its spatial inaccessibility for microorganisms after matrix flow while site specific properties did not significantly affect stabilisation. Instead, a more fine-textured site promotes the vertical transport of DOC due to a higher abundance of preferential flow paths.

中文翻译：

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山毛榉林下表土和底土中溶解有机碳的归宿和稳定性

来自 Oa 层的溶解有机碳 (DOC) 被认为是底土有机碳储量的重要贡献者。我们通过将 13C 标记的凋落物的 DOC 溶液直接注入山毛榉林地的三个土壤深度来研究 DOC 的命运。在注入后 3 个月和 17 个月，通过深钻至 2 m 深的土壤岩心量化注入 DOC 的命运。3 个月后保留了 27 ± 26% 的注射 DOC，17 个月后保留了 17 ± 22%。在注入深度以下的前 10 厘米处发现的保留 DOC 高达 70%，并且表土中的平均含量高于底土中的含量。17 个月后，表土中的 DOC 大部分丢失（- 19%），而底土中的 DOC 变化不大（- 4.4%）。数据表明在底土中注入的 DOC 高度稳定，站点之间没有差异。然而，孵化实验揭示的潜在矿化作用在表层土或底土中注入的 DOC 之间没有差异，这强调了与表土相比，底土中环境因素对于 DOC 稳定的重要性。我们得出的结论是，底土中 DOC 的稳定性主要是由其在基质流动后微生物在空间上的不可接近性所驱动的，而场地特定的特性并没有显着影响稳定性。相反，由于更丰富的优先流动路径，更精细纹理的站点促进了 DOC 的垂直传输。我们得出的结论是，底土中 DOC 的稳定性主要是由其在基质流动后微生物在空间上的不可接近性所驱动的，而场地特定的特性并没有显着影响稳定性。相反，由于更丰富的优先流动路径，更精细纹理的站点促进了 DOC 的垂直传输。我们得出的结论是，底土中 DOC 的稳定性主要是由其在基质流动后微生物在空间上的不可接近性所驱动的，而场地特定的特性并没有显着影响稳定性。相反，由于更丰富的优先流动路径，更精细纹理的站点促进了 DOC 的垂直传输。