Increased Earthworm Density Supports Soil Carbon Storage in a Forest Exposed to Elevated CO2

Carbon isotope analysis tracked carbon transfer from detritus to earthworms, earthworm casts, and soil.

The Science

The density of native earthworms in a sweetgum plantation forest increased in response to the stimulation of fine-root production caused by carbon dioxide (CO2) enrichment of the forest, and the earthworms altered the transfer of carbon from dead plant material to soil.

The Impact

This research has identified earthworm activity as an important mechanism for increased production of soil microaggregates and carbon accrual in response to increasing atmospheric CO2. Carbon accrual in protected soil pools removes carbon from the atmosphere and thereby partially mitigates the increasing concentration in the atmosphere.

Summary

Net primary productivity influences soil food webs and ultimately the amount of carbon inputs in ecosystems. Earthworms can physically protect organic matter from rapid mineralization through the formation of soil aggregates. Previous studies at the Oak Ridge National Laboratory Free Air CO2 Enrichment (FACE) experiment showed that elevated CO2 increased fine-root production and increased soil carbon through soil aggregation. In this project, the role of earthworms in these carbon transfer processes was investigated by tracking the stable carbon isotope signature in leaf litter, fine roots, earthworms, earthworm casts, and bulk soil. The most abundant endogeic (subsurface, organic matter–consuming) earthworm at the FACE site is Diplocardia spp., and its density was positively correlated with production of leaf litter and fine roots in the previous two years. Carbon isotope analysis following termination of the elevated CO2 treatment confirmed that the earthworms were consuming organic matter derived from previous years’ plant detritus. The positive response of earthworms to increased fine-root production, caused by CO2 enrichment, is consistent with the increased soil aggregate formation and increased soil carbon observed in the CO2-enriched plots of the FACE experiment.

Principal Investigator

Yaniria Sánchez-de León
University of Illinois at Chicago and University of Puerto Rico at Mayagüez
yaniria.sanchez@upr.edu

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

The Oak Ridge National Laboratory (ORNL) Free Air CO2 Enrichment (FACE) experiment was supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science. This work was funded by the National Science Foundation (grant #DEB-0919276), the University of Illinois at Chicago (UIC), the UIC Stable Isotope Laboratory, the University of Puerto Rico at Utuado (UPRU), and the University of Puerto Rico at Mayagüez.

Related Links

References

Sánchez-de León, Y., D. H. Wise, J. Lugo-Pérez, and R. J. Norby, et al.. "Endogeic earthworm densities increase in response to higher fine-root production in a forest exposed to elevated CO2". Soil Biology and Biochemistry 122 31–38  (2018). https://doi.org/10.1016/j.soilbio.2018.03.027.