Affiliation:
1. Department of Ecological Microbiology, University of Bayreuth, 95445 Bayreuth
2. Department of Bioremediation, Center for Environmental Research Leipzig-Halle, 04318 Leipzig, Germany
Abstract
ABSTRACT
Earthworms emit the greenhouse gas nitrous oxide (N
2
O), and ingested denitrifiers in the gut appear to be the main source of this N
2
O. The primary goal of this study was to determine if earthworms also emit dinitrogen (N
2
), the end product of complete denitrification. When [
15
N]nitrate was injected into the gut, the earthworms
Aporrectodea caliginosa
and
Lumbricus terrestris
emitted labeled N
2
(and also labeled N
2
O) under in vivo conditions; emission of N
2
by these two earthworms was relatively linear and approximated 1.2 and 6.6 nmol N
2
per h per g (fresh weight), respectively. Isolated gut contents also produced [
15
N]nitrate-derived N
2
and N
2
O under anoxic conditions. N
2
is formed by N
2
O reductase, and acetylene, an inhibitor of this enzyme, inhibited the emission of [
15
N]nitrate-derived N
2
by living earthworms. Standard gas chromatographic analysis demonstrated that the amount of N
2
O emitted was relatively linear during initial incubation periods and increased in response to acetylene. The calculated rates for the native emissions of N
2
(i.e., without added nitrate) by
A. caliginosa
and
L. terrestris
were 1.1 and 1.5 nmol N
2
per h per g (fresh weight), respectively; these emission rates approximated that of N
2
O. These collective observations indicate that (i) earthworms emit N
2
concomitant with the emission of N
2
O via the in situ activity of denitrifying bacteria in the gut and (ii) N
2
O is quantitatively an important denitrification-derived end product under in situ conditions.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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