| Wüst, PK; Horn, MA; Henderson, G; Janssen, PH; Rehm, B; Drake, HL: Gut-Associated Denitrification and In Vivo Emission of Nitrous Oxide by the Earthworm Families Megascolecidae and Lumbricidae in New Zealand, Applied and Environmental Microbiology, 75 (11), 3430-3436 (2009) | |
| Abstract: Previous studies have documented the capacity of European earthworms of the family Lumbricidae to emit the greenhouse gas nitrous oxide (N2O), an activity attributed primarily to the activation of ingested soil denitrifiers. To extend this information base to earthworms in the southern hemisphere, four different species of earthworms in New Zealand were examined for gut-associated denitrification. Lumbricus rubellus and Aporrectodea rosea (introduced species [Lumbricidae]) emitted N2O, whereas emission of N2O by Octolasion cyaneum (an introduced species [Lumbricidae]) and Octochaetus multiporus (a native species [Megascolecidae]) was variable and negligible, respectively. Exposing earthworms to nitrite or nitrate and acetylene significantly stimulated the amount of N2O emitted, implicating denitrification as the primary source of N2O, and likewise indicating that earthworms emitted dinitrogen (N2) in addition to N2O. The alimentary canal displayed a high capacity to produce N2O when supplemented with nitrite, and alimentary canal contents had high amounts of carbohydrates and organic acids indicative of fermentation (e.g., succinate, acetate, and formate) that could serve as sources of reductant for denitrification. NosZ genes encode for a portion of the terminal oxidoreductase in denitrification. NosZ sequences detected in the alimentary canals of L. rubellus and O. multiporus were similar to those retrieved from soil and were distantly related to uncultured soil bacteria and genera common to soils (i.e., Bradyrhizobium, Azospirillum, Rhodopseudomonas, Rhodospirillum, Pseudomonas, Oligotropha, and Sinorhizobium). These findings (a) suggest that the capacity to emit N2O and N2 is a generalized trait of earthworms and not geographically restricted, (b) indicate that species of different earthworm families (i.e., Megascolecidae vs. Lumbricidae) may not have equal capacities to emit N2O, and (c) also corroborate previous findings that link this capacity to denitrification in the alimentary canal. |
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