Abstract
<p>Recent compilations of global soil radiocarbon data suggest that current Earth System Models underestimate the mean age of soil carbon (C). The discrepancy between data-derived estimates and model calculations might be due to an inadequate representation of processes that control C persistence in soils – especially in understudied regions.</p><p>Here, we investigate the relationships between soil mineralogy, soil properties, climate and radiocarbon (Δ<sup>14</sup>C) in soils sampled as part of a comprehensive soil survey (AfSIS) for sub-Saharan Africa. A total of 510 samples were analyzed, comprised of soils collected from two depths (0–20 cm and 20–50 cm) at 30 sites in 14 countries. To determine soil mineralogy, we analyzed X-ray powder diffraction (XRPD) data, which provides a precise and detailed mineralogical signature of each soil sample. The studied soil profiles vary greatly in their mineralogy, reflecting a diverse range of parent materials and soil forming factors.</p><p>The median soil C age is 182 years in the topsoils and 563 years in the subsoils, corresponding to a total Δ<sup>14</sup>C value range of -432 to 95 ‰. In general, Δ<sup>14</sup>C values decrease (older mean C ages) with increasing clay particle size fractions. This corresponds to an increase in short range-order minerals expressed as oxalate-extractable aluminum and iron (Al<sub>ox</sub> and Fe<sub>ox</sub>). Separately, mineralogically defined variables – derived from the XRPD data using principal component analysis – are found to correlate strongly with a range of soil properties (pH, weathering status, exchangeable calcium, Al<sub>ox</sub> and Fe<sub>ox</sub>, and soil texture) and climatic variables (aridity index and mean annual temperature). This provides a holistic assessment of the processes that have formed each soil along with the properties that it currently exhibits. Our analyses with random forests show that these XRPD-derived mineralogical variables alone can explain up to 30% of the variation in Δ<sup>14</sup>C across sub-Saharan Africa. They also allow the identification of specific minerals that contribute to this variation and how they are linked to the C mean age of the soil. In conclusion, our results suggest that soil mineral data can help to better understand C persistence in subtropical and tropical soils.</p>
Highlights
This page was generated automatically upon download from the ETH Zurich Research Collection
Soil carbon persistence linked to mineralogy across subSaharan Africa
We investigate the relationships between soil mineralogy, soil properties, climate and radiocarbon (Δ C) in soils sampled as part of a comprehensive soil survey (AfSIS) for sub-Saharan Africa
Summary
This page was generated automatically upon download from the ETH Zurich Research Collection. Soil carbon persistence linked to mineralogy across subSaharan Africa Author(s): von Fromm, Sophie Franziska; Hoyt, Alison M.; Butler, Benjamin M.; Berhe, Asmeret Asefaw; Doetterl, Sebastian; Haefele, Stephan M.; McGrath, Steve P.; Shepherd, Keith D.; Six, Johan; Towett, Erick K.; Winowiecki, Leigh A.; Trumbore, Susan E.
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