Dynamics of carbon and nitrogen mineralization, microbial biomass, and nematode abundance within and outside the burrow walls of anecic earthworms (Lumbricus terrestris)

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We conducted a laboratory study using soil cores to determine whether anecic earthworm (Lumbricus terrestris) burrow linings (the drilosphere) are sites for enhanced carbon and nitrogen mineralization and increased microbial biomass and nematode abundance. We compared microbial biomass C, C mineralization rates, metabolic quotient, levels of inorganic N (NO3/- and NH4/+), and nematode abundance over the course of 11 weeks in soil from earthworm burrows, bulk soil away from burrows, and a control soil in cores to which no earthworms were added. Significant differences were observed in microbial biomass carbon, which was 38 to 84% lower, and carbon mineralization and metabolic quotient, which were 2.3 to 7.5 and 5.6 to 17.4 times, respectively, higher in burrow than in control soil. No significant differences were observed in these variables between bulk and control soil. In addition, nematodes were 3.7 to 6.5 times more abundant, and inorganic N levels 21 to 78% higher in burrow than in control soil, with no significant differences observed between bulk and control soil. Dynamics of microbial biomass carbon and inorganic N followed the same general pattern in burrow, bulk, and control soil. By contrast, dynamics of nematode abundance, carbon mineralization, and metabolic quotient differed between burrow and both bulk and control soil, with peak values observed at 5, 7, and 11 weeks for nematode abundance, C mineralization, and metabolic quotient, respectively. Our results suggest that earthworms may have an indirect effect on soil C and N dynamics by stimulating the activities of nematodes and their interaction with microbial biomass in the drilosphere to a greater degree than is observed in soil that has not come in direct contact with earthworms.

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Soil Science