Nitrous oxide in vivo emission may regulate nitrogen stoichiometry in earthworm body tissues

There is growing evidence that earthworms maintain strict homeostasis in their nitrogen (N) stoichiometry, but the mechanisms employed remain poorly understood. Herein, we examined whether the endogeic earthworm Aporrectodea turgida regulates N stoichiometry in its body (1) by changing the quantity of N excreted from urine and mucus secretion, and (2) regulating the amounts of N2O and N-2 emitted from their body by the aid of gutmicrobiota. These objectives were evaluated in a laboratory experiment using N-15-labeled adults of A. turgida and tracking the N-15 lost from their body during a 48 h period in microcosms containing soil-plant litter mixtures varying in N content and C:N ratio. The quantity of N-15 excreted by A. turgida after 48 h was about 3.7 +/- 0.3 mu g and was composed of 50% N-15-mineral N and 34% N-15-DON. The N excretion rate varied, on average, from 507 to 699 mu g N g(-1) fw d(-1) with no effect of the litter treatment (P > 0.05). It is unlikely that N release through urine and mucus regulated N stoichiometry in the body tissue of A. turgida. However, the net change in N2O production with earthworms and the quantity of N-15-N2O was 8-12 times greater in microcosms amended with the N-rich red clover than N-poor litters and the control (no litter). This suggests that in vivo N2O emission from A. turgida may regulate the N stoichiometry of its body tissues.