IMPACT OF EARTHWORM INVASION ON SOIL TEMPERATURE REGIME IN THE FENNOSCANDIAN ARCTIC

Global rise in temperatures due to carbon dioxide emissions have created an increased interest in monitoring the carbon cycle in arctic and boreal forests, which are estimated to contain 623 Pg, or 27% of global soil organic carbon. Exotic earthworm species have been introduced to these areas where earthworm species have not been known to exist since the most recent glacial period. It has been observed in boreal, arctic and temperate deciduous and coniferous ecosystems that certain introduced species can remove the organic soil horizons that make up the forest floor and create a deep A horizon, where the organic material is now in contact with mineral particles. Although many aspects of this dramatic change in soil structure have been studied, little work has been done to determine how the removal of the insulating O horizons affects soil temperature. Temperature sensors were installed at sites along two transects (invaded and non-invaded) near Jierpen, Sweden in forests dominated by Betula pubescens (arctic birch). Thickness of O horizon was used as criteria for selecting sites, and O horizon in non-invaded sites ranged from 8-15cm thick, while O horizon thickness in invaded sites ranged from 0-6.5cm thick. Sensors were installed at multiple depths: at the top of the soil profile, the start of the mineral surface (immediately below surface sensor if the organic layer is 0cm thick), and 10cm below the start of the mineral horizon. Temperatures were recorded from July 2018 to June 2019, at intervals of 255 minutes (4 hrs, 15 minutes). Our data shows that intact O horizons provide a significant insulating effect for the top 10cm of mineral soil layers (up to 13˚C during summer months). In addition, date of freezing was delayed by several days in non-invaded sites due to insulating effects. Not only do earthworms change the form of organic carbon in the soil, but they dramatically alter the soil temperature regime by removal of the insulating O horizons. This new temperature regime in the soil and altered soil carbon profiles after earthworm invasion will complicate predicting the fate of soil organic carbon in the arctic environment.