Effects of enchytraeids (Annelida: Oligochaeta) on soil carbon and nitrogen dynamics in laboratory incubations

Enchytraeids are abundant in many different agricultural systems. However, their role in decomposition processes and nitrogen mineralization is not well understood. This study was conducted to evaluate the influence of a common enchytraeid (Enchytraeus minutus, Nielsen and Christensen 1961) on these processes in two soils (sandy clay loam and loamy sand) under two different litter placement treatments (buried versus surface placed) in a laboratory experiment. Forty-five enchytraeids were added to half of the constructed jars. Every 4 weeks (up to 112 days) three jars of each soil-litter-enchytraeid treatment were destructively sampled for determination of enchytraeid abundance, microbial biomass, dissolved organic carbon (DOC), and floatable particulate organic matter (FLPOM)-C and -N. Soil respiration and N2O fluxes were measured at biweekly intervals. At the end of the experiment less DOC was present in the sandy clay loam treatments with enchytraeids. The influence of enchytraeids on denitrification rates, depended on soil texture and litter placement. In the Buried Litter treatment enchytraeids caused an increase in the N2O-flux in the loamy sand soil and a decrease in the sandy clay loam soil. Variation in the flux was large, therefore the differences in enchytraeid and non-enchytraeid treatments were not significant. Essentially no denitrification occurred in the Surface Litter treatments. Enchytraeids affected decomposition by decreasing the amount of floatable POM in the soils. They increased the mobilization of nitrogen, resulting in larger amounts of inorganic-N in the soil solution after 112 days. Through immobilization of nitrogen in their tissue and the subsequent release upon mortality, enchytraeids provided a large pulse of inorganic nitrogen in the sandy clay loam soil. In the loamy sand treatments where mortality was less, an increase in inorganic nitrogen due the activities of enchytraeids was also found at the end of the experiment. In this laboratory study enchytraeids significantly affected decomposition and nitrogen mineralization. High abundances of enchytraeids often correspond with the beginning of the growing season in Georgia; therefore, through enchytraeid activities, more nitrogen may be available for plant uptake. (C) 2003 Elsevier B.V. All rights reserved.