Carbon and Nitrogen Dynamics in Lumbricus terrestris (L.) Burrow Soil Relationship to Plant Residues and Macropores

The formation of macropores and litter translocation into burrows by anecic earthworms [Lumbricus terrestris (L.)] may be important in controlling the extent to which earthworms affect C and N dynamics. We conducted a mesocosmscale laboratory experiment to assess the relationship between corn (Zea mays L.) litter incorporation by L. terrestris and C and N dynamics in burrow soil. We also evaluated the relative contribution of macropores and litter incorporation to C and N dynamics in the burrow soil. Four treatments were employed: control (CTRL), artificial burrows (ARTF), artificial burrows containing corn leaves (LEAF), and amended with L. terrestris (WORM). We measured soil C and N, dissolved organic C, C mineralization, and ammonium and nitrate-N periodically, and litter removal and litter in burrows over 16 wk. A significant, short-lived enhancement in C mineralization and in soil C and N was observed in WORM and LEAF treatments. Inorganic N increased with incubation time only in the WORM treatment. Nitrate dominated the inorganic N pool in WORM and LEAF treatments, accumulating in both, and to a lesser extent in the ARTF treatment. Strong correlations were observed between litter remaining aboveground and C mineralization, ammonium-N, and nitrate-N in the WORM treatments, whereas only nitrate-N was correlated with litter resources in LEAF treatment. Our results indicate that C and N dynamics in the burrow soil of L. terrestris are coupled strongly to surface litter removal. Macropores and litter incorporation into macropores by themselves do not appear to explain the effects of L. terrestris on C and N dynamics in burrow soil.