Objective

Soil organic carbon (SOC) in deeper soils may be more protected by mineral particles than SOC in shallower soils; thus, the vertical SOC distribution is closely related to the overall SOC stability. This study aimed to verify the relationship between the solubility temperature dependence of water extractable SOC fractions and their vertical distribution characteristics.

Methods

Soil samples collected from each soil horizon in natural dragon spruce (Picea asperata) and red birch (Betula albosinensis) forests were analyzed. Cold water-extracted organic carbon (CWEOC) and hot water-extracted organic carbon (HWEOC) were extracted at 20 °C and 80 °C, respectively. The sum of CWEOC and HWEOC was considered the water-extracted organic carbon (WEOC) content. The carbohydrate-C (Car-C) and phenolic-C (Phe-C) contents extracted by hot water were also determined.

Results

The CWEOC, HWEOC, Car-C, and Phe-C contents varied significantly (P < 0.001) among soil horizons. The WEOC/SOC ratio increased significantly from the decomposed organic (H-) horizon to the surface mineral (A-) horizon (P < 0.05) but was not significantly different among the surface (A-), the subsurface (B-), and the bottom (C-) mineral horizons (Brunisols, according to the Canadian Soil Classification System). In both forests, CWEOC/HWEOC increased from the H- horizon to the B- horizon but was not significantly different between the B- and C- horizons. The Car-C/Phe-C ratios in the mineral soil horizons were significantly higher than those in the H-horizon and litter.

Conclusions

The more water-soluble SOC fractions tended to be more distributed in the deeper horizons. Therefore, WEOC in mineral soils may be more stable than is generally believed.

中文翻译：

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云杉和白桦林土壤剖面中水可提取有机碳组分的特征

客观的

与浅层土壤中的 SOC 相比，深层土壤中的土壤有机碳 (SOC) 可能更受矿物颗粒的保护；因此，垂直SOC分布与整体SOC稳定性密切相关。本研究旨在验证水可提取 SOC 组分的溶解度温度依赖性与其垂直分布特征之间的关系。

方法

分析了从天然云杉 ( Picea asperata ) 和红桦 ( Betula albosinensis ) 森林中每个土壤层收集的土壤样品。冷水萃取的有机碳 (CWEOC) 和热水萃取的有机碳 (HWEOC) 分别在 20 °C 和 80 °C 下萃取。CWEOC 和 HWEOC 的总和被认为是水提取的有机碳 (WEOC) 含量。还测定了热水提取的碳水化合物-C (Car-C) 和酚类-C (Phe-C) 含量。

结果

CWEOC、HWEOC、Car-C 和 Phe-C 含量 在土壤层间差异显着（P < 0.001）。WEOC/SOC 比从分解的有机物 (H-) 层到地表矿物 (A-) 层 显着增加( P < 0.05) 但在地表 (A-)、地下 (B-)、和底部 (C-) 矿物层（Brunisols，根据加拿大土壤分类系统）。在这两个森林中，CWEOC/HWEOC 从 H- 层级增加到 B- 层级，但 B- 和 C- 层级之间没有显着差异。矿质土壤层的 Car-C/Phe-C 比率显着高于 H 层和凋落物。

结论

水溶性越多的 SOC 部分往往分布在更深的地层中。因此，矿质土壤中的 WEOC 可能比人们普遍认为的更稳定。