Forest liming is a management tool that has and continues to be used extensively across northern Europe to counteract acidification processes from anthropogenic sulfur and nitrogen (N) deposition. In this study, we quantified how liming affects soil organic carbon (SOC) stocks and attempt to disentangle the mechanisms responsible for the often contrasting processes that regulate net soil carbon (C) fluxes. Using a paired plot experimental design we compared SOC stocks in limed plots with adjacent unlimed control plots at 28 experimental sites to 60 cm soil depth in mature broadleaf and coniferous forests across Germany. Historical soil data from a subset of the paired experiment plots were analyzed to assess how SOC stocks in both control and limed plots changed between 1990 and 2019.Overall, we found that forest floor C stocks have been accumulating over time in the control plots. Liming however largely offset organic layer buildup in the L/O_f layer, and forest floor C stocks remained unchanged over time in the limed plots. This, in turn, meant that nutrients remained mobile and were not bound in soil organic matter complexes. Results from the paired plot analysis showed that forest floor C stocks were significantly lower in limed plots than the control (−34 %, −8.4 ± 1.7 Mg C ha⁻¹) but did not significantly affect SOC stocks in the mineral soil, when all sites are pooled together. In the forest floor layers, SOC stocks exhibited an exponential decrease with increasing pH, highlighting how lime-induced improvements in the biochemical environment stimulate organic matter (OM) decomposition. Nevertheless, for both forest floor and mineral soils, the magnitude and direction of the belowground C changes hinged directly on the inherent site characteristics, namely, forest type (conifer versus broadleaf), soil pH, soil texture, and the soil SOC stocks. On the other hand, SOC stock decreases were often offset by other processes that fostered C accumulation, such as improved forest productivity or increased carbon stabilization, which correspondingly translated to an overall variable response by SOC stocks, particularly in the mineral soil.Lastly, we measured soil carbon dioxide (CO₂) and soil methane (CH₄) flux immediately after a re-liming event at three of the experimental sites. Here, we found that (1) liming doubles CH₄ uptake in the long-term; (2) soil organic matter mineralization processes respond quickly to liming, even though the duration and size of the CO₂ flush varied between sites; and (3) lime-derived CO₂ contributed very little to total CO₂ emissions over the measurement period (determined using stable isotope approaches).

中文翻译：

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面对气候变化的森林施石灰：恢复性施石灰对德国成熟森林土壤有机碳的影响

森林施石灰是一种管理工具，已经并将继续在整个北欧广泛使用，以抵消人为硫和氮 (N) 沉降造成的酸化过程。在这项研究中，我们量化了施石灰对土壤有机碳 (SOC) 储量的影响，并试图理清负责调节净土壤碳 (C) 通量的经常对比过程的机制。我们使用成对样地实验设计，比较了德国各地成熟阔叶林和针叶林中 28 个实验地点 60 厘米土壤深度的施石灰样地与相邻未施石灰对照样地的 SOC 储量。对来自配对试验地块子集的历史土壤数据进行了分析，以评估 1990 年至 2019 年间对照地块和石灰地块的 SOC 储量如何变化。总体而言，我们发现，随着时间的推移，控制地块的森林地面碳储量一直在积累。然而，石灰在很大程度上抵消了 L/O 中的有机层堆积_f层和林地碳储量在石灰地块中随时间保持不变。反过来，这意味着养分保持流动，不受土壤有机质复合物的束缚。配对地块分析的结果表明，施石灰地块的森林地面碳储量显着低于对照（ - 34 %， - 8.4  ±  1.7  Mg C ha ^-1) 但当所有地点汇集在一起​​时，并未显着影响矿质土壤中的 SOC 库存。在森林地面层中，SOC 储量随着 pH 值的增加呈指数下降，突出表明石灰诱导的生化环境改善如何刺激有机物 (OM) 分解。然而，对于森林地面和矿质土壤，地下 C 变化的幅度和方向直接取决于固有的立地特征，即森林类型（针叶树与阔叶树）、土壤 pH 值、土壤质地和土壤 SOC 储量。另一方面，SOC 库的减少通常被其他促进碳积累的过程所抵消，例如提高森林生产力或增加碳稳定性，​​这相应地转化为 SOC 库的整体变量响应，CO ₂ ) 和土壤甲烷 ( CH ₄ ) 在三个实验地点重新施石灰事件后立即通量。在这里，我们发现 (1) 石灰处理使CH ₄的长期吸收加倍；(2) 土壤有机质矿化过程对石灰处理反应迅速，尽管CO ₂冲洗的持续时间和规模因地点而异；(3)在测量期间（使用稳定同位素方法确定），石灰衍生的CO ₂对总CO ₂排放量的 贡献非常小。