Effect of the endogeic earthworm Aporrectodea tuberculata on aggregation and carbon redistribution in uninvaded forest soil columns

Abstract

a b s t r a c tThe long-term impact of earthworm presence on soil carbon (C) dynamics of previously uninhabited northeastern forests is still largely unknown. Currently, earthworm presence is understood to both enhance soil respiration and create stable microaggregates, processes assumed to have conflicting effects on long term C storage. To date, studies investigating earthworm-created microaggregates and occluded C have rarely been done in undisturbed forest soils. A paired mesocosm study (n ¼ 5) was conducted investigating the impact of the endogeic earthworm species Aporrectodea tuberculata on the physical proportion of microaggregates and the associated mineral soil C of a minimally disturbed forest soil. Pairs analyzed after 4 weeks of incubation demonstrated no significant aggregate effects. At 4 months, paired cores with earthworms (WW) showed a 67% increase in large macroaggregates (>2000 mm diameter, lgMA), compared to cores without earthworms (NW). While distribution shifted among various microaggregate pools (free and occluded within macroaggregates), the net proportion of microaggregates in the soil (dry weight basis) was unaltered. After 4 months, the mineral soil of WW cores had an average of 60% more C than the NW cores due to the relocation of the forest floor. The C associated with the microaggregate fractions increased an average of 56%. Of this increase in C, 95% was accounted for by the microaggregates occluded within the lgMA fraction, a fraction that was almost 4 times greater in the WW cores. Over 50% of the C relocated into the mineral soil was associated with the physically protected microaggregate fractions, indicating that though this species of earthworm did not alter the proportion of microaggregates in these soils, they occluded a substantial proportion of C within those physical fractions. In this particular forest soil, the actions of Aporrectodea tuberculata increased the physically protected C pool through microaggregate restructuring and C enrichment.

Soil chemistry turned upside down: a meta‐analysis of invasive earthworm effects on soil chemical properties

“…We found lower C content in organic soil invaded by earthworms compared to uninvaded soil, but not in mineral soil. This finding is in line with previous studies, where earthworms were found to fix a considerable part of soil C in earthworm casts and stable organo‐mineral complexes (Martin , Scheu and Wolters , Bohlen et al , Knowles et al ). Indeed, most of the studies in our meta‐analysis only considered the residual (i.e., nonstable) plant available C. However, such stabilization effects may have been negligible in mineral soil as compared to mixing effects.…”

Root litter decomposition slows with soil depth

“…Another potential mechanism for slower decomposition of roots in the coarse particulate fraction is the lack of soil fauna at depth that can increase litter surface area via fragmentation (Knowles et al, 2016) and the delivery of labile substrates by creating preferential flow paths. The abundance of bioturbation agents like arthropods generally declines steeply with depth (Jiménez and Decaëns, 2000; Petersen and Luxton, 1982).…”

Impact of different earthworm ecotypes on water stable aggregates and soil water holding capacity

“…2). This could be because the contribution of earthworm mucus to organic binding agents (Knowles et al 2016;Schomburg et al 2018) or the stimulation of fungal activity via the increased supply of soluble organic compounds (Montecchio et al 2015;Parle 1963;Rashid et al 2016) is more significant in low-organic matter soils. Alternatively, or additionally, the earthworm activity may have a bigger impact on aggregate formation where there are more clay-sized particles available for aggregation.…”