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Depletion of soil carbon and aggregation after strong warming of a subarctic Andosol under forest and grassland cover
Soil ( IF 6.8 ) Pub Date : 2020-03-23 , DOI: 10.5194/soil-6-115-2020
Christopher Poeplau , Páll Sigurðsson , Bjarni D. Sigurdsson

The net loss of soil organic carbon (SOC) from terrestrial ecosystems is a likely consequence of global warming and may affect key soil functions. The strongest changes in temperature are expected to occur at high northern latitudes, with forest and tundra as prevailing land cover types. However, specific soil responses to warming in different ecosystems are currently understudied. In this study, we used a natural geothermal soil warming gradient (0–17.5 C warming intensity) in an Icelandic spruce forest on Andosol to assess changes in the SOC content between 0 and 10 cm (topsoil) and between 20 and 30 cm (subsoil) after 10 years of soil warming. Five different SOC fractions were isolated, and their redistribution and the amount of stable aggregates were assessed to link SOC to changes in the soil structure. The results were compared to an adjacent, previously investigated warmed grassland. Soil warming depleted the SOC content in the forest soil by −2.7 g kg−1C−1 (−3.6 % C−1) in the topsoil and −1.6 g kg−1C−1 (−4.5 % C−1) in the subsoil. The distribution of SOC in different fractions was significantly altered, with particulate organic matter and SOC in sand and stable aggregates being relatively depleted and SOC attached to silt and clay being relatively enriched in warmed soils. The major reason for this shift was aggregate breakdown: the topsoil aggregate mass proportion was reduced from 60.7±2.2 % in the unwarmed reference to 28.9±4.6 % in the most warmed soil. Across both depths, the loss of one unit of SOC caused a depletion of 4.5 units of aggregated soil, which strongly affected the bulk density (an R2 value of 0.91 and p<0.001 when correlated with SOC, and an R2 value of 0.51 and p<0.001 when correlated with soil mass in stable aggregates). The proportion of water-extractable carbon increased with decreasing aggregation, which might indicate an indirect protective effect of aggregates larger than 63 µm on SOC. Topsoil changes in the total SOC content and fraction distribution were more pronounced in the forest than in the adjacent warmed grassland soils, due to higher and more labile initial SOC. However, no ecosystem effect was observed on the warming response of the subsoil SOC content and fraction distribution. Thus, whole profile differences across ecosystems might be small. Changes in the soil structure upon warming should be studied more deeply and taken into consideration when interpreting or modelling biotic responses to warming.

中文翻译:

森林和草地覆盖下北极亚雄烷的强烈变暖后土壤碳的耗竭和聚集

陆地生态系统的土壤有机碳净损失是全球变暖的可能结果,并可能影响关键的土壤功能。温度的最强烈变化预计将发生在北部高纬度地区,其中森林和冻原为主要的土地覆盖类型。但是,目前尚未研究土壤对不同生态系统变暖的具体反应。在这项研究中,我们使用了天然地土壤增温梯度(0-17.5  C变暖强度)在冰岛Andosol上的云杉林中,以评估土壤变暖10年后SOC含量在0至10 cm(表土)和20至30 cm(底土)之间的变化。分离出五种不同的SOC组分,并对其重新分布和稳定聚集体的数量进行了评估,以将SOC与土壤结构的变化联系起来。将结果与相邻的先前研究过的温暖草地进行了比较。土壤变暖由贫森林土壤的SOC含量-2.7 克千克-1 Ç -1-3.6  %  Ç -1)在表土和-1.6 克千克-1 Ç -1-4.5  %  Ç -1)在底土。SOC在不同部分的分布发生了显着变化,沙粒中的有机物和SOC以及稳定的骨料中的SOC相对减少,而附着在粉砂和粘土上的SOC在温暖的土壤中相对富集。发生这种变化的主要原因是骨料分解:表土的骨料质量比例  从未加温的参考值的60.7±2.2%降至 最温暖的土壤的28.9±4.6%。在这两个深度上,SOC损失一单位会导致4.5单位聚集土壤的消耗,这严重影响了堆密度(R 2值为0.91,p <0.001与SOC相关时, R 2值为0.51,与稳定团聚体中的土壤质量相关时p <0.001。吸水碳的比例随着聚集体的减少而增加,这可能表明大于63 µm的聚集体具有间接的保护作用。 SOC上的m。由于初始SOC较高且较不稳定,与相邻的温暖草地土壤相比,森林中总SOC含量和分数分布的表土变化更为明显。但是,没有观察到生态系统对土壤下层SOC含量和馏分分布的升温响应的影响。因此,整个生态系统的整体轮廓差异可能很小。在解释或模拟生物对变暖的响应时,应更深入地研究变暖后土壤结构的变化,并加以考虑。
更新日期:2020-03-23
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