Invasive Earthworms and Forest Successional Stage Interact to Impact Plant Litter Inputs and Particulate Organic Matter Chemistry

Authors: CROW, S - PURDUE UNIVERSITY; FILLEY, T - PURDUE UNIVERSITY; MCCORMICK, M - SMITHSONIAN ENV RES CTR; SZLAVECZ, K - JOHN HOPKINS UNIVERSITY; Stott, Diane; GAMBLIN, D - PURDUE UNIVERSITY; CONYERS, G - PURDUE UNIVERSITY

Submitted to: Biogeochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2008
Publication Date: 2/20/2009
Citation: Crow, S.E., Filley, T.R., McCormick, M., Szlavecz, K., Stott, D.E., Gamblin, D., Conyers, G. 2009. Invasive Earthworms and Forest Successional Stage Interact to Impact Plant Litter Inputs and Particulate Organic Matter Chemistry. Biogeochemistry. 92:61-82.

Interpretive Summary: The landscapes colonized by invasive earthworm in the eastern U.S. are often patchworks of forest stands in various stages of successional development. We established six field sites in tulip poplar forests in the Smithsonian Environmental Research Center Forest, MD (SERC), that span young (50-70 yrs old; three plots) and old (>150 yrs old; three plots) successional stages where young sites had a higher earthworm density and biomass than the old and were dominated by non-native earthworm species. Previous results at SERC documented that in the areas of high earthworm abundance, the leaf resides of the tulip poplar became enriched in lignin-like phenols (six carbon ring structured compounds) during the decomposition process, while residues from low earthworm sites were enriched in aliphatic (straight chains of carbon) material. This lead to a hypothesis that the soil organic matter (SOM) from these sites would reflect the changes in remnant residues, impacting the ease that the SOM itself can be degraded. From the bulk soil, we isolated the soil particulate organic matter (POM) by a combination of size and density fractionations. This fraction of the SOM consists primarily of root and buried residue material in various stages of decomposition. We found that the patterns of the POM chemistry were indeed similar to what was previously found in the decayed tulip poplar litter: in the older forests, where the earthworms were less abundant, the POM fraction had relatively more aliphatic compounds, fewer lignin-like phenolic compounds, and the ratio of aliphatic-to-phenolic ratio was greater when compare to the younger forests where non-native earthworms were more abundant. However, the chemistry of litter from young versus old successional tree species did not explain all the differences seen in POM chemistry. Differences in the initial root and leaf chemistry were also primary drivers of POM chemistry in young versus old sites, indicating that preferential feeding by the earthworms on leaf body tissue caused subsequent shifts in available aliphatic compounds. These results indicate that invasive earthworm activity in North American forests can shift the composition of POM, the most active fraction of the SOM, and thus potentially influence C dynamics and stabilization of C in soil. This work impacts forest managers and ecologists dealing with invasive worm species and their influence on the forest health. It also impacts those studying the C cycle, as invasive worm species alter the chemistry of the SOM and carbon availability.

Technical Abstract: The landscapes colonized by invasive earthworms in the eastern U.S. are often patchworks of forest stands in various stages of successional development. We established six field sites in tulip poplar dominated forests in the Smithsonian Environmental Research Center Forest (SERC), MD, that span young (50-70 yrs-three plots) and old (>150 yrs-three plots) successional stages where young sites had a higher earthworm density and biomass than the old and were dominated by non-native lumbricid species. Previous results at SERC documented a clear chemical trajectory during tulip poplar leaf decay that was driven by high earthworm abundance in the young sites. In high earthworm sites tulip poplar litter residue was relatively enriched in CuO extractable lignin phenols (SVC-lignin) while in low earthworm sites the residues were enriched in cutin derived aliphatic material. We separated particulate organic matter (POM) from the bulk soil by a combination of size and density fractionations and found that patterns in POM chemistry were similar to those found previously during litter decay: in older forests, where earthworms were less abundant, substituted fatty acid (SFA) concentration was greater, SVC-lignin lower, and the SFA-to-SVC-lignin ratio greater than in younger forests where earthworm activity was high. The chemistry of litter from young versus old successional tree species did not explain the differences in POM chemistry between young and old sites. Instead, the differences in root and leaf chemistry were the primary drivers of POM chemistry in young versus old sites, indicating that preferential feeding on leaf body tissue and the subsequent shifts in source of SFA in soil influenced differences in POM chemistry between old and young forests. These results indicate that invasive earthworm activity in North American forests can shift the aromatic and aliphatic composition of litter residue and thus potentially influence C dynamics and stabilization in soil. This work impacts forest managers and ecologists dealing with invasive worm species and their influence on the forest health. It also impacts those studying the C cycle, as invasive worm species alter the chemistry of the soil and C availability.