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Earthworms Contribute to the Terrestrial Cycling of Carbon and Nitrogen via Fermentation and Denitrification in the Alimentary Canal

Pia K. Wüst1, Marcus A. Horn1, Harold L. Drake1
1 Department of Ecological Microbiology

O 1.6 in Ecosystem Function

02.04.2009, 11:45-12:00, H8

The in situ conditions of the earthworm gut, which include anoxia, high water content, a near-neutral pH, and high concentrations of organic compounds, have been proposed to selectively stimulate ingested soil microorganisms.  Thus, potential links between in situ conditions and anaerobic microbial activities during gut passage of Lumbricus terrestris were evaluated.  H2 and N2O were emitted in vivo, and in situ microsensor analyses revealed H2 and N2O as concomitant products in the anoxic gut center.  H2 concentrations were highest in foregut and midgut, whereas N2O concentrations were highest in crop/gizzard and hindgut.  Thus, H2-producing fermentations were maximal in the foregut and midgut whereas denitrification was maximal in crop/gizzard and hindgut.  Total organic carbon and nitrite decreased from anterior to posterior of the alimentary canal. Concentrations of polymeric and soluble saccharides decreased from the anterior to the posterior end of the alimentary canal.  Maximal concentrations of organic acids occurred in the midgut, indicating that fermentation is ongoing during gut passage.  These findings suggest that (a) ingested microorganisms are subject to changing in situ conditions during gut passage, (b) fermentation and denitrification occur concomitantly along the alimentary canal (c) the alimentary canal of the earthworm is a hotspot in aerated soils for carbon- and nitrogen-driven anaerobiosis, and (d) earthworms are a mobile source of reductant (i.e., emitted H2) for microbiota in aerated soils.

last modified 2009-03-06