Carbon dioxide and nitrous oxide fluxes from soil as influenced by anecic and endogeic earthworms

Earthworm-microbial interactions may stimulate CO2 and N2O emissions from soil. This study examined the influence of anecic and endogeic earthworms, represented by Lumbricus terrestris L. and Aporrectodea caliginosa Savigny, on CO2 and N2O fluxes, and on the processes (denitrification, nitrification) that lead to N2O flux from an agricultural soil. Laboratory microcosms, with and without earthworms, were incubated at 15 degrees C and 40% water-filled pore space, and headspace gases were sampled after 1, 4, 7, 14, 21, and 28 days. Denitrification and nitrification processes were then evaluated in a 24 h acetylene inhibition experiment. Earthworms were responsible for 7-58% of the total CO2 flux from soil, compared to the control (no earthworms), but did not affect the N2O flux. The CO2 flux was greater when more earthworms were present, and in microcosms with mixed L. terrestris and A. caliginosa populations, suggesting that microbial respiration could be stimulated by the interactions of anecic and endogeic earthworms. Denitrification was the dominant process leading to N2O production from microcosms with L. terrestris, while nitrification was more important in microcosms with A. caliginosa. Microcosms with mixed populations produced more N2O from denitrification than nitrification. Species-specific stimulation of nitrifiers and denitrifiers may be related to unique structures (casts, burrows) produced by L. terrestris and A. caliginosa, but this remains to be confirmed. (c) 2007 Elsevier B.V. All rights reserved.