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<p>The radiocarbon content of soil organic carbon (C) is assumed to reflect the carbon’s biological reactivity. Large soil radiocarbon ages are interpreted to mean that the C will have a slow response to environmental perturbations such as the effects of warming on the soil microbial C decomposition rate. Here we show that downward advective transport of soil C is an important process affecting soil C ages, leading to an inevitable increase in radiocarbon age with depth even if the decomposition rates remain constant. Thus, the increasing radiocarbon ages of C with depth do not directly imply a corresponding decrease in C reactivity as a function of depth. On the basis of theory and an independent assessment of soil C decomposition rates, the radiocarbon profiles (and content for a given depth) were calculated for over 3,000 soils in the USA and were compared to observational results based on measured soil radiocarbon. The first-order coherence between the two entirely differing approaches suggests the fundamental importance of transport and the implication that the soil C decomposition rate constant may be relatively invariant with depth. These insights may serve to reduce biases in Earth system models that presently do not match the observed depth patterns in soil C or its radiocarbon content.</p>

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Neglecting vertical transport leads to underestimated soil carbon dynamics

  • 期刊论文

  • 发表日期：

    2025年12月8日

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  • Ronald Amundson,
  • Jonathan Sanderman,
  • Kyungsoo Yoo,
  • Maedeh Chitsaz,
  • Anna Abramova,
  • Katerina Georgiou

摘要

The radiocarbon content of soil organic carbon (C) is assumed to reflect the carbon’s biological reactivity. Large soil radiocarbon ages are interpreted to mean that the C will have a slow response to environmental perturbations such as the effects of warming on the soil microbial C decomposition rate. Here we show that downward advective transport of soil C is an important process affecting soil C ages, leading to an inevitable increase in radiocarbon age with depth even if the decomposition rates remain constant. Thus, the increasing radiocarbon ages of C with depth do not directly imply a corresponding decrease in C reactivity as a function of depth. On the basis of theory and an independent assessment of soil C decomposition rates, the radiocarbon profiles (and content for a given depth) were calculated for over 3,000 soils in the USA and were compared to observational results based on measured soil radiocarbon. The first-order coherence between the two entirely differing approaches suggests the fundamental importance of transport and the implication that the soil C decomposition rate constant may be relatively invariant with depth. These insights may serve to reduce biases in Earth system models that presently do not match the observed depth patterns in soil C or its radiocarbon content.