ABSTRACT The biological recalcitrance or decomposability of soil organic carbon (SOC) determines its lability and thus C cycling in an ecosystem. Many studies of temperate and tropical soils have reported that SOC from deeper soil is older and more recalcitrant than surface soil. However, it is not clear whether this trend holds for arctic tundra soils. We report results of C isotope measurements and incubation experiments of selected soil samples to determine the relationship between SOC decomposition and its age. Soil organic carbon content was greater in surface soil layers than deeper layers. The 14C age of SOC ranged from modern near the surface to 6,920 years before present at the depth of 87 to 105 cm. However, the SOC of the frozen or deep layer (>20 cm) was also biologically labile compared to the top active layer. Our data reveal that for arctic tundra soils the relationship between the age of SOC and its recalcitrance is opposite to the trend for most temperate and tropical soils, indicating that deep permafrost carbon is highly vulnerable to decomposition in response to climate warming and arctic coastal erosion.

中文翻译：

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沿阿拉斯加北部侵蚀海岸线的土壤有机碳反应性

摘要 土壤有机碳 (SOC) 的生物顽固性或可分解性决定了其不稳定性，从而决定了生态系统中的碳循环。许多关于温带和热带土壤的研究报告称，深层土壤中的 SOC 比表层土壤更古老、更顽固。然而，目前尚不清楚这种趋势是否适用于北极苔原土壤。我们报告了选定土壤样品的 C 同位素测量结果和孵化实验，以确定 SOC 分解与其年龄之间的关系。表层土壤有机碳含量高于深层土壤。SOC 的 14C 年龄范围从现代近地表到 6,920 年之前的 87 至 105 厘米深度。然而，与顶部活性层相比，冷冻层或深层 (>20 cm) 的 SOC 也是生物不稳定的。