Effects of Lumbricus terrestris L. on nitrogen dynamics beyond the burrow

The degree to which earthworms can affect the availability of plant nutrients depends on their distribution following formation in burrow soil. We conducted a mesocosm-scale laboratory experiment to test the hypothesis that anecic earthworms (those that build semi-permanent vertical burrows) can affect C and N dynamics beyond the confines of the soil immediately surrounding their burrows. Nitrate and ammonium concentrations and the rate of C mineralization were determined in burrow (defined as soil within 5 mm from the macropore wall, regardless of its origin) and bulk soil of treatments amended with Lumbricus terrestris (WORM) and in treatments containing artificial burrows (ARTF) and artificial burrows containing corn leaves (LEAF) periodically over the course of 16 weeks. Comparisons were made to soil in unamended treatments (CTRL) under two different moisture regimes, WET and DRY, during the course of the experiment. Nitrate concentration was significantly higher in WORM and LEAF bulk soil than in CTRL soil, but only under WET conditions. Differences in nitrate concentrations appeared after incubation for 5 weeks and persisted for 11 weeks. Ammonium concentration and C mineralization in bulk soil were not significantly different from CTRL soil for any of the treatments regardless of moisture regime, although values for both variables were significantly higher in burrow than in bulk soil in WORM and LEAF treatments. Anecic earthworms can enhance nitrate concentrations in soil beyond the confines of the burrow, a process that appears to be facilitated with increased soil moisture.