BayCEER Workshop 2008

Anaerobic activities and in situ N2O concentrations along the alimentary canal of the earthworm Lumbricus terrestris

Earthworms constitute the dominant soil macrofauna in many soils and emit nitrous oxide (N₂O) concomitantly to nitrogen (N₂). The production of N₂O and N₂ by earthworms is due to their gut microbiota. Microsensor profiles for crop & gizzard indicated that in situ N₂O concentrations were highest in the center. Single-point measurements for crop & gizzard, foregut, midgut, and hindgut revealed that highest in situ N₂O concentrations occurred in crop & gizzard and in hindgut. Earthworm sections containing either crop & gizzard or hindgut emitted highest amounts of N₂O and N₂ relative to fore- and midgut containing sections. The emission of N₂ was always higher than the emission of N₂O. Moisture content, total carbon, and total nitrogen were highest in the foregut and decreased from the anterior to the posterior end of the gut. Nitrite, ammonium, and iron(II) were highest in crop & gizzard and decreased from the anterior to the posterior end of the alimentary canal. Concentrations of soluble organic compounds differed along the alimentary canal. Highest concentrations of glucose (5 mM), N-acetylglucosamine (1 mM), and lactate (26 mM) were detected in crop & gizzard. Succinate (3 mM), methylbutyrate (9 mM), and formate (17 mM) primarily occurred in the midgut. Butyrate (7 mM) and acetate (9 mM) dominated in mid- and hindgut. Collective results suggest that (i) crop & gizzard are hotspots of fermentations, denitrification, and Fe(III)-reduction, (ii) complete denitrification and fermentations are active along the alimentary canal, and (iii) fermentation derived organic acids might represent trophic links to denitrification and Fe(III)-reduction.