Soil Moisture and Temperature: Tolerances and Optima for a Non-Native Earthworm Species,Amynthas agrestis(Oligochaeta: Opisthopora: Megascolecidae)

Field observations indicate an invasion by the non-native, Asian earthworm species Amynthas agrestis (Goto and Hatai 1899) in the Great Smoky Mountains National Park (GSMNP). The aim of this study was to determine if A. agrestis was capable of surviving in the ridge-top soil along an invasion front in a mesic—xeric habitat gradient in GSMNP. Additionally, this study sought to determine optimum and tolerance conditions for A. agrestis within a range of soil moistures and temperatures. Investigating soil temperature and moisture as parameters of earthworm survivability will allow for more predictive power when investigating the GSNMP invasion. Although A. agrestis invasions are widespread in eastern North America, few studies have addressed factors that may influence their distribution and their potential impacts on ecosystem processes. Using incubators and PVC tube microcosms, it was determined that A. agrestis was able to survive in the GSMNP ridge-top soil at temperatures of 12 °C and 25 °C. No survival was observed at temperatures of-5, 5, or 35 °C at any soil moisture level. No survival occurred in 25 °C dry (8% gravimetric water) treatments. Of the conditions tested, maximum survival plus fresh-weight maintenace occured at 12 °C and mid-moisture (24% gravimetric water), but highest activity and effects on litter and soil structure occurred at 25 °C and high soil moisture (57% gravimetric water; field capacity). Soil moisture contributed to the success of A. agrestis at higher temperatures within the tolerance conditions; more moisture increased the survival rate and decreased weight-loss.