Heterotrophic soil respiration is an important component of the global terrestrial carbon (C) cycle, driven by environmental factors acting from local to continental scales. For tropical Africa, these factors and their interactions remain largely unknown. Here, using samples collected along topographic and geochemical gradients in the East African Rift Valley, we study how soil chemistry and fertility drive soil respiration of soils developed from different parent materials even after many millennia of weathering. To address the drivers of soil respiration, we incubated soils from three regions with contrasting geochemistry (mafic, felsic and mixed sediment) sampled along slope gradients. For three soil depths, we measured the potential maximum heterotrophic respiration under stable environmental conditions and the radiocarbon content (Δ¹⁴C) of the bulk soil and respired CO₂. Our study shows that soil fertility conditions are the main determinant of C stability in tropical forest soils. We found that soil microorganisms were able to mineralize soil C from a variety of sources and with variable C quality under laboratory conditions representative of tropical topsoil. However, in the presence of organic carbon sources of poor quality or the presence of strong mineral-related C stabilization, microorganisms tend to discriminate against these energy sources in favour of more accessible forms of soil organic matter, resulting in a slower rate of C cycling. Furthermore, despite similarities in climate and vegetation, soil respiration showed distinct patterns with soil depth and parent material geochemistry. The topographic origin of our samples was not a main determinant of the observed respiration rates and Δ¹⁴C. In situ, however, soil hydrological conditions likely influence soil C stability by inhibiting decomposition in valley subsoils. Our results demonstrate that, even in deeply weathered tropical soils, parent material has a long-lasting effect on soil chemistry that can influence and control microbial activity, the size of subsoil C stocks and the turnover of C in soil. Soil parent material and its control on soil chemistry need to be taken into account to understand and predict C stabilization and rates of C cycling in tropical forest soils.

中文翻译：

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地球化学特征不同的非洲热带森林土壤中的异养土壤呼吸和碳循环

异养土壤呼吸是全球陆地碳（C) 循环，由从地方到大陆尺度的环境因素驱动。对于热带非洲，这些因素及其相互作用在很大程度上仍然未知。在这里，我们使用沿东非大裂谷的地形和地球化学梯度收集的样本，研究即使经过数千年的风化，土壤化学和肥力如何驱动由不同母体材料发育的土壤的土壤呼吸。为了解决土壤呼吸的驱动因素，我们培养了来自三个具有对比地球化学（镁铁质、长英质和混合沉积物）沿坡度梯度采样的区域的土壤。对于三个土壤深度，我们测量了稳定环境条件下的潜在最大异养呼吸和散装土壤的放射性碳含量 ( Δ ¹⁴ C ) 和呼吸一氧化碳₂。我们的研究表明，土壤肥力条件是 热带森林土壤中碳稳定性的主要决定因素。我们发现土壤微生物能够在代表热带表土的实验室条件下矿化来自各种来源的土壤碳，并具有不同的碳质量。然而，在存在质量差的有机碳源或存在与矿物相关的强C 稳定性的情况下，微生物倾向于歧视这些能源，而偏向于更容易获得的土壤有机质形式，导致C速率降低 骑自行车。此外，尽管气候和植被相似，但土壤呼吸在土壤深度和母质地球化学方面表现出不同的模式。我们样品的地形起源不是观察到的呼吸率和Δ ¹⁴ C的主要决定因素。然而，就地土壤水文条件可能 通过抑制山谷底土的分解来影响土壤碳的稳定性。我们的研究结果表明，即使是在深度风化的热带土壤，母质对土壤化学性质的持久效果，可以影响和控制微生物的活动，地下的大小Ç 股票，成交额Ç在土壤中。需要考虑土壤母质及其对土壤化学的控制，以了解和预测  热带森林土壤中的碳 稳定和碳循环速率。