Stability of Soil Organic Carbon: Impacts of Particle Size


Studies comparing the mineralization rate of organic carbon (C) associated with different particle size fractions are extremely limited. Organic C associated with the mineral fraction, in particular, is thought to have long residence times. Studies of C decomposition as a function of particle size should improve the representation of long-term C stabilization processes in terrestrial carbon cycle models. A recent study at Oak Ridge National Laboratory sought to quantify decomposition of native soil organic C and a newly added C substrate from both particulate and mineral soil pools. Five different soils were fractionated into particulate (> 53 µm) and mineral (< 53 µm) fractions, radiolabeled with glucose, and incubated for 150 days. Results indicated that the mineralization of native soil organic C was higher from the particulate fraction than the mineral fraction, while mineralization of glucose was similar from both fractions. Furthermore, native organic C in the soil mineral fraction was observed to be resistant to decomposition, in contrast to added glucose which was readily decomposed. Glucose additions therefore appear to be an inadequate surrogate for quantifying long residence times of organic C associated with soil minerals. Although we currently lack adequate experimental data on mineral-associated fractions, this study represents a significant step toward improving our understanding of long-term C stability of soil organic matter and representing these mechanisms in ecosystem-scale models.


Jagadamma, S., J. M. Steinweg, M. A. Mayes, G. Wang, and W. M. Post. 2013. “Decomposition of Added and Native Organic Carbon from Physically Separated Fractions of Diverse Soils,” Biology and Fertility of Soils, DOI:10.1007/s00374-013-0879-2.