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Melnichuk, Ryan Dustin Scott

Plant and Soil Science

2016

PhD

Anthropogenic activities surrounding horticulture, agriculture and recreation have increased dispersal of invasive earthworms. The introduction of earthworms initiates many physical and chemical alterations in forest soils previously unoccupied by earthworms. Three trials were performed to assess the effects of earthworms on soil-water dynamics, C and N and defensive/storage compound production by a native plant. The first trial was a greenhouse experiment, performed to assess the impact of two ecologically contrasting invasive earthworm species on percolate and evaporative soil water loss. Mesocosms were constructed to simulate a typical forest Entisol commonly penetrated by the species of interest, Lumbricus terrestris and Amynthas agrestis. Earthworms were added in pair and combination to replicate an average population density observed in Vermont. Percolate water was collected and evaporative water loss balance was recorded over a period of 140 days. C and N were quantified in A-horizon bulk and aggregate soil as well as the subsoil. Residual surface leaf litter was also quantified. Results indicated significantly increased evaporative water loss where either worm was present. Conversely, percolate water loss was significantly reduced in presence L. terrestris alone. C and N analysis revealed that only L. terrestris had a significant effect on aggregate soil C. While the abundance of many herbaceous species is reduced at invasive earthworm sites, Arisaema triphyllum anecdotally have greater densities where earthworms are present. It has been hypothesized that the greater density is caused by a trait that allows this plant to store Ca, often observed at increased concentrations in earthworm invaded soils as Ca-oxalate Here, we tested the hypothesis that oxalate increases in A. triphyllum when earthworms are present. As such, we conducted a two-way factorial greenhouse trial to test whether the changes to soil properties made by two invasive earthworm species (Amynthas agrestis and Lumbricus rubellus) or their physical presence (and bioturbation) had an effect on the plant production of oxalate. Upon quantification of variable soluble oxalate in corms after senescence, we found that earthworm presence increased water soluble and total oxalate significantly as well as marginally significantly in the case of HCl soluble oxalate. No significant changes in oxalate concentrations were observed under soil treatments alone. Carbon and nitrogen are found extensively in both terrestrial and atmospheric cycles. A shift in the equilibrium of these elements can suggest a strong interaction between an introduced variable (invasive earthworms in this case) and the abiotic environment. To better understand changes in soil properties with earthworm invasion, a 112-day mesocosm study was undertaken to examine C and N dynamics. Two epi-endogeic invasive earthworm species Lumbricus rubellus and Amynthas agrestis were selected for study. Greenhouse gas production by total mesocosm and soil were monitored. Gas flux measurements on 11 dates indicate both worm species increase CO2 and N2O emitted from mesocosm system as well as soil. Mesocosm total C and N (mass balance) indicate significantly more N but no change in C where earthworms are present. This indicates a disruption of denitrification by earthworm invasion that results in increased N2O emissions. This research is the first to examine these variables in concert and confirms holistic view is essential when examining natural systems.