Understanding the controls on the amount and persistence of soil organic carbon (C) is essential for predicting its sensitivity to global change. The response may depend on whether C is unprotected, isolated within aggregates, or protected from decomposition by mineral associations. Here, we present a global synthesis of the relative influence of environmental factors on soil organic C partitioning among pools, abundance in each pool (mg C g−1 soil), and persistence (as approximated by radiocarbon abundance) in relatively unprotected particulate and protected mineral-bound pools. We show that C within particulate and mineral-associated pools consistently differed from one another in degree of persistence and relationship to environmental factors. Soil depth was the best predictor of C abundance and persistence, though it accounted for more variance in persistence. Persistence of all C pools decreased with increasing mean annual temperature (MAT) throughout the soil profile, whereas persistence increased with increasing wetness index (MAP/PET) in subsurface soils (30–176 cm). The relationship of C abundance (mg C g−1 soil) to climate varied among pools and with depth. Mineral-associated C in surface soils (<30 cm) increased more strongly with increasing wetness index than the free particulate C, but both pools showed attenuated responses to the wetness index at depth. Overall, these relationships suggest a strong influence of climate on soil C properties, and a potential loss of soil C from protected pools in areas with decreasing wetness. Relative persistence and abundance of C pools varied significantly among land cover types and soil parent material lithologies. This variability in each pool's relationship to environmental factors suggests that not all soil organic C is equally vulnerable to global change. Therefore, projections of future soil organic C based on patterns and responses of bulk soil organic C may be misleading.
|Title||Beyond bulk: Density fractions explain heterogeneity in global soil carbon abundance and persistence|
|Authors||Katherine Heckman, Caitlin E. Hicks Pries, Corey Lawrence, Craig Rasmussen, Susan E. Crow, Alison M. Hoyt, Sophie F. von Fromm, Zheng Shi, Shane Stoner, Casey McGrath, Jeffery Beem-Miller, Asmeret Asefaw Berhe, Joseph C. Blankinship, Marco Keiluweit, Erika Marín-Spiotta, J. Grey Monroe, Alain F. Plante, Joshua Schimel, Carlos A. Sierra, Aaron Thompson, Rota Wagai|
|Publication Subtype||Journal Article|
|Series Title||Global Change Biology|
|Record Source||USGS Publications Warehouse|
|USGS Organization||Geosciences and Environmental Change Science Center|