Earthworms Affect Forest Soil Carbon Stabilization
The role of soils in mitigating increases in atmospheric carbon dioxide (CO2) is uncertain, in part due to the complex biotic and abiotic interactions determining soil carbon change. Earthworms, in particular, interact with the physical and chemical protection mechanisms of organic matter, major determinants of carbon storage capacity of soils. Protection of enhanced plant litter inputs from rapid decomposition by soil aggregates was a key mechanism facilitating the carbon gain observed in surface soils of the sweetgum forest Free-Air CO2 Enrichment (FACE) experiment in Oak Ridge, TN. To evaluate whether two earthworm species with different feeding behaviors played a role in soil aggregate formation and the stabilization of leaf and/or root litter in these aggregates, Department of Energy researchers conducted a laboratory incubation experiment with earthworms plus isotopically labeled soil and plant materials from the sweetgum FACE site. Compared to the experimental treatments without worms, the presence of either earthworm species increased the formation of soil macroaggregates (greater than 250 µm in diameter). The invasive European earthworm species, which feeds on both plant residues and soil organic matter, incorporated significant amounts of leaf- and root-derived carbon, in addition to soil-derived carbon, into newly formed aggregates. In contrast, the native earthworm species, which feeds mostly on soil organic matter, produced almost twice as many aggregates, but hardly any of the carbon in these aggregates was derived from the added plant materials. Overall, these findings suggest that the presence or absence of earthworms—and specifically the type of earthworm—could be an important factor contributing to the fate of increased plant litter produced as a result of rising atmospheric CO2 concentrations.
Sánchez-de León, Y., J. Lugo-Pérez, D. H. Wise, J. D. Jastrow, and M. A. González-Meler. 2014. “Aggregate Formation and Carbon Sequestration by Earthworms in Soil from a Temperate Forest Exposed to Elevated Atmospheric CO2: A Microcosm Experiment,” Soil Biology and Biochemistry 68, 223–30. DOI:10.1016/j.soilbio.2013.09.023.