Pyrogenic carbon (PyC) is produced by the incomplete combustion of vegetation during wildfires and is a major and persistent pool of the global carbon (C) cycle. However, its redistribution in the landscape after fires remains largely unknown. Therefore, we conducted rainfall simulation experiments on 0.25 m² plots with two distinct Swiss forest soils (Cambisol (clay loam) and Luvisol (sandy silt)). We applied PyC produced from wood (Picea abies) labeled under FACE conditions and C₄ grass (Miscanthus sinensis) to the soil surface to study PyC redistribution by runoff and splash and the vertical mobility of PyC in a 10 cm unsaturated soil column based on the differences in δ¹³C of soils and PyC. We assessed the effect of soil texture, slope angle and PyC characteristics (feedstock and particle size) on the mobility of PyC during 30 min of intense rainfall (102 mm h⁻¹). Our results highlight that PyC is highly mobile. Surface runoff transported between 0.2 % and 36.0 % of the total added PyC. Erosion by splash further redistributed 10.3 % to 25.3 % of the added PyC. Soil type had a substantial impact on the redistribution of PyC by both runoff and splash: on average, we recovered 10.5 % of the added PyC in runoff and splashed material for the clay-rich Cambisol and 61.3 % of the added PyC for the sandy silt Luvisol combined. PyC feedstock had a clear but contrasting effect on PyC redistribution: relocation in the runoff and splashed material was greater for wood PyC (43.4 % of total added PyC) than grass PyC (28.4 %). However, more wood PyC (11.5 %; fraction of organic C derived from the PyC) remained where it was initially applied compared to grass PyC (7.4 %). The results further suggest that the effect of PyC characteristics on its mobility can be highly variable and depend not only on the material from which it was derived, but also on other factors (e.g., particle size, porosity, density). In particular, the mobility of PyC was almost twice as large for fine-grained PyC (< 63 µm) than for coarse PyC (63 µm–2 mm). Vertical mobility of PyC up to 10 cm depth was greater in the clay-rich, well-aggregated Cambisol but limited in the physically instable Luvisol, likely due to quick aggregate breakdown and surface sealing. The addition of PyC to the surface of the studied soils further induced changes in the export of native soil organic carbon (nSOC) after the 30 min rainfall event. Our study shows that large quantities of PyC can be redistributed by water erosion over short timescales and that the mobility of PyC depends to a great extent on the response of soils to rainfall. Moreover, the addition and redistribution of PyC affects the export of nSOC and thus the C budget of fire-affected soils and catchments.

中文翻译：

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模拟降雨事件中热解碳再分配的关键驱动力

火成碳（PyC）是由野火期间植被的不完全燃烧产生的，是全球碳（C）循环的主要且持续的池。然而，大火后其在景观中的重新分布仍然未知。因此，我们在0.25 m ²地块上使用两种不同的瑞士森林土壤（Cambisol（粘土壤土）和Luvisol（桑迪淤泥））进行了降雨模拟实验。我们将FACE条件下标记的木材（Picea abies）和C ₄草（Miscanthus sinensis）产生的PyC应用于土壤表面，以研究PyC在10cm的非饱和土壤柱中基于径流和飞溅的重新分布和垂直迁移率。在不同δ ¹³C和PyC。我们评估了30分钟的强降雨（102 mm h ^-1）下土壤质地，坡度角和PyC特性（原料和粒径）对PyC迁移率的影响。。我们的结果表明，PyC具有高度的移动性。地表径流的传输量为添加的PyC总量的0.2％至36.0％。飞溅侵蚀进一步将10.3％的PyC重新分配到25.3％。土壤类型对径流和飞溅物对PyC的重新分布都有重大影响：平均而言，我们回收了径流和飞溅物中富含粘土的Cambisol的PyC的10.5％，以及对沙质淤泥的PyC的61.3％。卢维索合并。PyC原料对PyC的重新分配具有明显但相反的影响：径流和飞溅物料中的迁移比木材PyC（占总添加PyC的43.4％）要大得多，比草PyC（28.4％）大。但是，与草木PyC（7.4％）相比，最初使用的木料PyC（11.5％；来自PyC的有机碳的比例）得以保留。结果进一步表明，PyC特性对其迁移率的影响可能是高度可变的，不仅取决于其来源，还取决于其他因素（例如，粒径，孔隙率，密度）。特别是，PyC的迁移率几乎是细颗粒PyC的两倍（<  63  μ M）比粗的PyC（63  μ M-2毫米）。在富含粘土，聚集良好的坎比索尔中，PyC的垂直迁移率在10 cm深度处更大，但在物理不稳定的Luvisol中则受到限制，这可能是由于聚集体快速分解和表面密封所致。在30分钟的降雨事件之后，向研究土壤的表面添加PyC会进一步引起天然土壤有机碳（nSOC）出口的变化。我们的研究表明，PyC可以在短时间内通过水蚀而重新分布，并且PyC的流动性在很大程度上取决于土壤对降雨的响应。此外，添加和重新分配 PyC的变化会影响nSOC的出口，从而影响受火灾土壤和集水区的C预算。