Earthworms, stand age, and species composition interact to influence particulate organic matter chemistry during forest succession

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 in Edgewater, MD, that span mid (50-70 years-three plots) and late (120-150 years-three plots) successional stages where younger sites had greater earthworm density and biomass than older sites and were dominated by nonnative lumbricid species. In particular Lumbricus rubellus, a litter-feeding species, was abundant in mid successional forests. Here, we separated particulate organic matter (POM) from the bulk soil by a combination of size and density fractionation and found that patterns in soil POM chemistry were similar to those found previously during litter decay: in younger forests with high abundance of earthworms, organic carbon normalized cutin-and suberinderived substituted fatty acid (SFA) concentration was lower and lignin-derived phenols greater than in older forests where earthworms were less abundant. The chemistry of the dominant litter from mid versus late successional tree species did not fully explain the differences in POM chemistry between age classes. Instead, the differences in leaf body versus petiole and leaf versus root chemistry were the dominant drivers of POM chemistry in mid versus late successional stands, although aspects of stand age and tree species also impacted POM chemistry. Our results indicate that preferential ingestion of leaf body tissue by earthworms and the subsequent shifts in sources of plant biopolymers in soil influenced POM chemistry in mid successional forests. These results indicate that invasive earthworm activity in North American forests contributes to a shift in the aromatic and aliphatic composition of POM and thus potentially influences carbon stabilization in soil.

Historical land use and stand age effects on forest soil properties in the Mid-Atlantic US

“…The uncut forests are dominated by several species of oak (Quercus) with the dominant species being chestnut oak (Q. prinus) which contributes 70% of the total litter input (Szlavecz unpublished data). Previous research by our group has demonstrated that nonnative earthworms are an important component of SERC forests (Crow et al, 2009;Filley et al, 2008;Ma et al, 2013;Szlavecz and Csuzdi, 2007;Szlavecz et al, 2011). In the context of this study, the uncut forests on Hog Island, Fox Point and Big Island are earthworm-free while non-native earthworms are abundant in soils at the old and young forest stands (Szlavecz and Csuzdi, 2007;Szlavecz et al, 2011).…”

Chemical characteristics of particulate organic matter from a small, mountainous river system in the Oregon Coast Range, USA

“…Because different types of vascular plants synthesize these compounds in characteristic patterns; cutin acids (CA) provide another unique tracer of vegetationderived carbon in a variety of settings (e.g., Gough et al 1993;Kastner and Goñi 2003;Sollins et al 2006;Crow et al 2009b). Suberin, another aliphatic polymer associated with root tissues of vascular plants, also produces substituted fatty acids (primarily x-hydroxyhexadecanoic, hexadecanedioic acid, and x-hydroxyoctadecenoic acid; e.g., Crow et al 2009a). …”

“…The contrasts between these two macromolecules indicate marked differences in the character and transport of vegetation-derived POM (i.e., woody versus nonwoody plant matter) as a function of discharge. Examination of the individual hydroxylated fatty acid data showed compounds with a predominant suberin origin (e.g., Crow et al 2009a) accounted for less than 10% of combined hydroxyfatty acid yields measured. Furthermore, all fine and coarse samples displayed dihydroxyhexadecanoic acid/x-hydroxyoctadecenoic acid ratios much greater than 60, indicating most of these hydroxyl fatty acids in the rivers suspended materials originated from above ground tissues (e.g., needles and leaves) rather than below ground (e.g., roots) sources (Filley et al 2008).…”

Land use history alters the relationship between native and exotic plants: the rich don’t always get richer

“…Japanese stilt grass (Microstegium vimineum), for example, is an annual plant and thus completely reliant on annual seed set to maintain populations. Furthermore, younger and more disturbed forests at SERC and elsewhere are also more highly invaded by exotic earthworms (Gundale et al 2005;Crow et al 2009), and the intensive grazing of surface organic material by earthworms can also contribute to increased soil compaction (Hale et al 2005) and thus potentially to exotic plant invasions.…”