Abstract
Soil organic carbon (SOC) can be stabilized via association with iron (Fe) and aluminum (Al) minerals. Fe and Al can be strong predictors of SOC storage and turnover in soils with relatively high extractable metals content and moderately acidic to circumneutral pH. Here we test whether pedogenic Fe and Al influence SOC content and turnover in soils with low Fe and Al content and acidic pH. In soils from four sites spanning three soil orders, we quantified the amount of Fe and Al in operationally-defined poorly crystalline and organically-complexed phases using selective chemical dissolution applied to the soil fraction containing mineral-associated carbon. We evaluated the correlations of Fe and Al concentrations, mean annual precipitation (MAP), mean annual temperature (MAT), and pH with SOC content and 14C-based turnover times. We found that poorly crystalline Fe and Al content predicted SOC turnover times (p < 0.0001) consistent with findings of previous studies, while organically-complexed Fe and Al content was a better predictor of SOC concentration (p < 0.0001). Greater site-level MAP (p < 0.0001) and colder site-level MAT (p < 0.0001) were correlated with longer SOC turnover times but were not correlated with SOC content. Our results suggest that poorly crystalline Fe and Al effectively slow the turnover of SOC in these acidic soils, even when their combined content in the soil is less than 2% by mass. However, in the strongly acidic Spodosol, organo-metal complexes tended to be less stable resulting in a more actively cycling mineral-associated SOC pool.
Original language | English |
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Pages (from-to) | 333-345 |
Number of pages | 13 |
Journal | Biogeochemistry |
Volume | 133 |
Issue number | 3 |
DOIs | |
State | Published - May 1 2017 |
Funding
The authors gratefully acknowledge EBIS AmeriFlux Project Donald E. Todd and Jana Phillips for the field collection of samples at the EBIS sites. We thank study site contacts Bill Munger, Dave Hollinger, Steve Pallardy, and Jim LeMoine who provided valuable information on site characterization and site data and Joern T. Larsen and April T. Van Hise for expert assistance with ICP-MS analysis. This work was supported by the United States Department of Energy, Office of Science, Office of Biological and Environmental Research under Contract No. DE-AC02-05CH11231 to Berkeley Lab; and under project SCW0676 to Lawrence Livermore National Laboratory (under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344).
Keywords
- C
- Mineral-organic associations
- Selective chemical dissolution
- Soil carbon stabilization
- Soil fractionation
- Soil organic carbon