Authors
Marie Spohn
Published in
Global change biology. Volume 32. Issue 9. Pages e71107.
Abstract
Soil organic matter (SOM) persistence and the SOM carbon-to-nitrogen (C:N) ratio determine long-term nitrogen (N) sequestration in terrestrial ecosystems. Yet, the question of how SOM persistence is related to the C:N ratio of SOM is still not fully resolved. Based on a global dataset on Δ14C in soils, I tested the hypothesis that SOM persistence is negatively correlated with the C:N ratio because N is enriched relative to carbon (C) as SOM ages. The results of this study demonstrate that the soil Δ14C decreased with decreasing C:N ratio, indicating that old, persistent SOM has a low C:N ratio, as hypothesized. The relationship between Δ14C and the C:N ratio had a breakpoint at a C:N ratio of approximately 13, indicating that organic matter with a high C:N ratio decomposes quickly, while SOM with a C:N ratio below 13 decomposes substantially more slowly. The Δ14C was higher in forest and shrubland soils than in grassland and cropland soils throughout the soil profile. High soil Δ14C values were associated with high soil C:N ratios in topsoil layers of forests and shrublands, suggesting that high inputs of plant detritus with high C:N ratios keep the C:N ratio elevated in the topsoil layers of these ecosystems. In conclusion, this study shows that old SOM has a low C:N ratio, indicating that organic N is preferentially retained in soils compared to organic C. The results have important implications for element cycling and soil C sequestration because they show that N is stored on average for longer periods in soils compared to C and that an increase in the amount of organic C that is sequestered in soils over centuries would strongly increase the amount of sequestered N.
PMID:
42768769
Bibliographic data and abstract were imported from PubMed on 22 Sep 2026.
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