Improved understanding of land use derived changes in soil organic matter (OM) compartments stabilized to different degrees against microbial decomposition is required for outlining efficient land use strategies aimed at improving soil ecosystem functions that are strongly coupled to gains and losses of soil organic carbon (OC). However, such data is scarce, particularly in subsoil environments. Consequently, in this study, we analyzed OC storage in topsoils and subsoils, as well as OM fractions with different OC turnover dynamics, including particulate (free and occluded), water-extractable, and mineral-associated OM. We sampled soils under native prairie (10 sites) and long-term arable use (> 40 years, 10 sites) to a depth of 3 m in the central U.S. Our results showed that the arable bulk soils had significantly lower OC content in the A horizon and across all analyzed OM fractions compared to native prairie soils. This reduction was primarily derived from OC losses in the mineral-associated OM (arable: 7.2 ± 0.5 g kg−1; native prairie: 12 ± 0.7 g kg−1), which retained the most significant portion (50–56 %) of bulk soil OC among all fractions. No significant impact of land use on OC storage in the bulk soil and fractions was observed in the subsoil B and C horizons, except for water-extractable OM, which had lower amounts in arable soils in the C horizon than native prairie soils. This underscores the relevance of this fraction for the translocation of OC across the soil profile in undisturbed systems. Our results highlight the crucial role of mineral-associated OM for soil OC storage, but also its sensitivity to land use change, especially in the topsoil, suggesting this fraction is highly relevant for strategies aiming at restoring pre-disturbance soil OC levels.

中文翻译：

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土地利用选择性地影响土壤碳储存，包括颗粒、水可萃取和矿物相关形式的土壤碳储存


需要更好地了解土壤有机质 （OM） 区室中在不同程度上稳定以抵抗微生物分解的土地利用衍生的变化，以概述旨在改善与土壤有机碳 （OC） 的得失密切相关的土壤生态系统功能的有效土地利用策略。然而，此类数据很少，尤其是在底土环境中。因此，在这项研究中，我们分析了表土和底土中的 OC 储存，以及具有不同 OC 周转动力学的 OM 组分，包括颗粒（游离和封闭）、水可萃取和矿物相关 OM。我们在美国中部的原生草原（10 个地点）和长期耕地使用（x3E 40 年，10 个地点）下取样，深度为 3 m。我们的结果表明，与原生草原土壤相比，可耕地块状土壤在 A 层和所有分析的 OM 组分中的 OC 含量显着降低。这种减少主要来自矿物相关 OM（耕地：7.2 ± 0.5 g kg-1;原生草原：12 ± 0.7 g kg-1）中的 OC 损失，它保留了所有组分中最重要的部分 （50-56%） 的散装土壤 OC。在底土 B 和 C 层中未观察到土地利用对块状土壤和组分中 OC 储存的显着影响，但可水提取的 OM 除外，它在 C 层的耕地土壤中的含量低于原生草原土壤。这强调了该部分与 OC 在未受干扰系统中土壤剖面上易位的相关性。我们的结果强调了矿物相关 OM 对土壤 OC 储存的关键作用，以及它对土地利用变化的敏感性，尤其是在表层土壤中，这表明该部分与旨在恢复干扰前土壤 OC 水平的策略高度相关。