Soil organic carbon (SOC) stabilization and destabilization has been studied intensively. Yet, the factors which control SOC content across scales remain unclear. Earlier studies demonstrated that soil texture and geochemistry strongly affect SOC content. However, those findings primarily rely on data from temperate regions where soil mineralogy, weathering status and climatic conditions generally differ from tropical and subtropical regions. We investigated soil properties and climate variables influencing SOC concentrations across sub-Saharan Africa. A total of 1601 samples were analyzed, collected from two depths (0–20 and 20–50 cm) from 17 countries as part of the Africa Soil Information Service project (AfSIS). The data set spans arid to humid climates and includes soils with a wide range of pH values, weathering status, soil texture, exchangeable cations, extractable metals and land cover types. The most important SOC predictors were identified by linear mixed-effects models, regression trees and random forest models. Our results indicate that geochemical properties, mainly oxalate-extractable metals (Al and Fe) and exchangeable Ca, are equally important compared to climatic variables (mean annual temperature and aridity index). Together, they explain approximately two-thirds of SOC variation across sub-Saharan Africa. Oxalate-extractable metals were most important in wet regions with acidic and highly weathered soils, whereas exchangeable Ca was more important in alkaline and less weathered soils in drier regions. In contrast, land cover and soil texture were not significant SOC predictors on this large scale. Our findings indicate that key factors controlling SOC across sub-Saharan Africa are broadly similar to those in temperate regions, despite differences in soil development history.

中文翻译：

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整个撒哈拉以南非洲大陆对土壤有机碳的控制

土壤有机碳 (SOC) 的稳定和去稳定已得到深入研究。然而，跨尺度控制 SOC 含量的因素仍不清楚。早期的研究表明，土壤质地和地球化学强烈影响 SOC 含量。然而，这些发现主要依赖于温带地区的数据，这些地区的土壤矿物学、风化状况和气候条件通常与热带和亚热带地区不同。我们调查了影响撒哈拉以南非洲 SOC 浓度的土壤特性和气候变量。作为非洲土壤信息服务项目 (AfSIS) 的一部分，从 17 个国家的两个深度（0-20 和 20-50 厘米）收集了总共 1601 个样本。该数据集跨越干旱到潮湿的气候，包括具有广泛 pH 值、风化状态、土壤质地、可交换阳离子、可提取金属和土地覆盖类型。最重要的 SOC 预测因子由线性混合效应模型、回归树和随机森林模型确定。我们的结果表明，与气候变量（年平均温度和干旱指数）相比，地球化学性质，主要是可提取草酸盐的金属（Al 和 Fe）和可交换的 Ca，同样重要。它们一起解释了撒哈拉以南非洲大约三分之二的 SOC 变化。草酸盐可萃取金属在酸性和高度风化土壤的潮湿地区最重要，而可交换钙在干燥地区的碱性和风化程度较低的土壤中更为重要。相比之下，土地覆盖和土壤质地在如此大的范围内并不是重要的 SOC 预测因子。