Effect of Lumbricus Rubellus and Amynthas Agrestis Earthworms on Soil Biogeochemistry at the Aggregate Scale in Northern Hardwood Forests

Abstract

Invasive earthworms can increase both pH and the nitrate concentrations in northern hardwood forests while nitrification is an acidification source. To obtain the nitrogen deposition impact, the soil pH, Ca, greenhouse gas emissions, and inorganic nitrogen forms have been compared for NH4+-N added and not added spodosol soils at aggregate scale inhabited by Amynthas agrestis (A) (ivasive/non-calciferous), Lumbricus rubellus (R) (non-invasive/calciferous), or no earthworm (C). Soils were classified into the three earthworm treatments by Naive Bayes classification using all gas emissions, Ca, and pH (misclassification rate of 9.3%). There were significant differences among the earthworm treatments in pH, Ca, N2O, and CO2 emissions. pH varied among earthworm treatments (A < C < R) and reduced over time for all three treatments. Water-soluble Ca and N2O emissions were greater in R than in A soils. Both earthworm treatments had greater NO3-N concentrations than the control. Stepwise regression identified Ca (4 out of 5 incubations, positive effect, explaining 11% to 26% of pH variance) and CO2 evolution (4 out of 5 incubations, negative effect 4% to 47% of pH variance) as the two most consistent predictors of pH. We consider the earthworm invasion may be an alternative buffering agent for the nitrogen deposition for forests.