Forest soils are fundamental in regulating the global carbon (C) cycle; their capacity to accumulate large stores of C means they form a vital role in mitigating the effects of climate change. Understanding the processes that regulate forest soil C dynamics and stabilisation is important to maximise the capacity and longevity of C sequestration. Compared with surface soil layers, little is known about soil C dynamics in subsoil layers, sensu those below 30 cm depth. This knowledge gap creates large uncertainties when estimating the distribution of global soil C stocks and assessing the vulnerability of soil C reserves to climate change. This study aimed to dive deep into the subsoils of Puruki Experimental Forest (New Zealand) and characterise the changes in soil C dynamics and the soil microbiome down to 1 m soil depth. ITS and 16S rRNA sequencing and quantitative real-time PCR were used to measure changes in soil microbial diversity, composition, and abundance. Stable (δ¹³C) and radioactive (¹⁴C) C analyses were performed to assess depth-driven changes in the stability and age of soil C. Our research identified large declines in microbial diversity and abundance with soil depth, alongside significant structural shifts in community membership. Importantly, we conservatively estimate that more than 35 % of soil C stocks are present in subsoil layers below 30 cm. Although the age of soil C steadily increased with depth, reaching a mean radiocarbon age of 1571 yr BP (years before present) in the deepest soil layers, the stability of soil C varied between different subsoil depth increments. These research findings highlight the importance of quantifying subsoil C stocks for accurate C accounting. By performing a broad range of analytical measures, this research has comprehensively characterised the abiotic and biotic properties of a subsoil environment – a frequently understudied but significant component of forest ecosystems.

中文翻译：

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土壤深度作为人工林（辐射松）浮石土中微生物和碳动态的驱动因素

森林土壤是调节全球碳 (C) 循环的基础；它们积累大量碳的能力意味着它们在减轻气候变化的影响方面发挥着至关重要的作用。了解调节森林土壤碳动态和稳定的过程对于最大化碳封存的能力和寿命很重要。与地表土层相比，人们对底土层土壤碳动态知之甚少，sensu那些在 30 厘米深度以下。在估算全球土壤碳储量的分布和评估土壤碳储量对气候变化的脆弱性时，这种知识差距造成了很大的不确定性。本研究旨在深入研究 Puruki 实验林（新西兰）的底土，并描述土壤碳动态变化和土壤微生物群落至 1 m 土壤深度的变化。ITS 和 16S rRNA 测序和定量实时 PCR 用于测量土壤微生物多样性、组成和丰度的变化。稳定 ( δ ¹³ C) 和放射性 ( ¹⁴C) 进行 C 分析以评估土壤 C 稳定性和年龄的深度驱动变化。我们的研究发现微生物多样性和丰度随着土壤深度的增加而大幅下降，同时社区成员的结构发生重大变化。重要的是，我们保守估计超过 35% 的土壤碳储量存在于 30 厘米以下的底土层中。尽管土壤 C 的年龄随着深度的增加而稳步增加，在最深的土壤层中达到 1571 年 BP（现在之前的几年）的平均放射性碳年龄，但土壤 C 的稳定性在不同的底土深度增量之间有所不同。这些研究结果强调了量化地下碳库对于准确计算碳的重要性。通过执行广泛的分析措施，