Denitrifying bacteria in the earthworm gastrointestinal tract and in vivo emission of nitrous oxide (N2O) by earthworms

Earthworms (Lumbricus rubellus and Octolasium lacteum) and gut homogenates did not produce CH4, and methanogens were not readily culturable from gut material. In contrast, the numbers of culturable denitrifiers averaged 7 x 10(7) and 9 x 10(6) per g (dry weight) of gut material for L. rubellus and O. lacteum, respectively; these values were 256- and 35-fold larger than the numbers of culturable denitrifiers in the soil from which the earthworms were obtained. Anaerobically incubated earthworm gut homogenates supplemented with nitrate produced N2O at rates exceeding that of soil homogenates, Furthermore, living earthworms emitted N2O under aerobic conditions, and N2O emission was stimulated bg acetylene. For earthworms collected from a mildly acidic (pH 6) beech forest soil, the rates of N2O emission for earthworms and soil averaged 884 and 2 pmol per h per g (fresh weight), respectively, In contrast, for earthworms collected from a more acidic (pH 4,6) oak-beech. forest soil, N2O emission bg earthworms and soil averaged 145 and 45 pmol pel h per g (fresh weight), respectively. Based on the extrapolation of this data, earthworms accounted for an estimated 16 and 0.25% of the total N2O produced at the stand level of these beech and oak-beech forest soils, respectively.