Abstract. Predicting the quantity of soil organic carbon (SOC) requires understanding how different factors control the amount of SOC. Land use has a major influence on the function of the soil as a carbon sink, as shown by substantial organic carbon (OC) losses from the soil upon deforestation. However, predicting the degree to which land use change affects the OC content in soils and the depth down to which this occurs requires context-specific information related to, for example, climate, geochemistry, and land use history. In this study, 266 samples from forests and agricultural fields were collected from 94 soil profiles down to 300 cm depth in a subtropical region (Arvorezinha, southern Brazil) to study the impact of land use on the amount of stabilized OC along the soil profile. We found that the stabilized OC content was not affected by land use below a depth of 90 cm. Along the soil profile, the amount of stabilized OC was predominantly controlled by land use and depth in addition to the silt and clay content and aluminium ion concentrations. Below 100 cm, none of the soil profiles reached a concentration of stabilized OC above 50 % of the stabilized OC saturation point (i.e. the maximum OC concentration that can physically be stabilized in these soils). Based on these results, we argue that it is unlikely that deeper soil layers can serve as an OC sink over a timescale relevant to global climate change due to the limited OC input in these deeper layers. Furthermore, we found that the soil weathering degree was not a relevant control on the amount of stabilized OC in our profiles because of the high weathering degree of the studied soils. It is therefore suggested that, while the soil weathering degree might be an effective controlling factor of OC stabilization over a large spatial scale, it is not an informative measure for this process at regional and local scales (with similar climate, bedrock, and weathering history) in highly weathered soils.

中文翻译：

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森林砍伐对亚热带流域稳定的地下有机碳的有限影响


摘要。预测土壤有机碳 (SOC) 量需要了解不同因素如何控制 SOC 量。土地利用对土壤作为碳汇的功能有重大影响，森林砍伐后土壤中有机碳（OC）大量损失就表明了这一点。然而，预测土地利用变化影响土壤中有机碳含量的程度以及这种影响发生的深度需要与气候、地球化学和土地利用历史等相关的特定背景信息。在这项研究中，从亚热带地区（巴西南部的 Arvorezinha）94 个深度达 300 厘米的土壤剖面中采集了 266 个来自森林和农田的样本，以研究土地利用对沿土壤剖面的稳定有机碳含量的影响。我们发现稳定的有机碳含量不受 90 厘米深度以下土地利用的影响。沿着土壤剖面，除了淤泥和粘土含量以及铝离子浓度之外，稳定OC的量主要受土地利用和深度控制。在 100 cm 以下，没有一个土壤剖面的稳定 OC 浓度达到稳定 OC 饱和点（即这些土壤中可以物理稳定的最大 OC 浓度）50%以上。基于这些结果，我们认为较深的土壤层不太可能在与全球气候变化相关的时间尺度上充当有机碳汇，因为这些较深层的有机碳输入有限。此外，我们发现，由于所研究土壤的风化程度较高，土壤风化程度并不是我们剖面中稳定OC含量的相关控制因素。 因此，建议虽然土壤风化程度可能是大空间尺度上OC稳定的有效控制因素，但它并不是区域和局部尺度上这一过程的信息量度（具有相似的气候、基岩和风化历史） ）在高度风化的土壤中。