Earthworm Influence On Nitrous Oxide Emissions Under Constant and Fluctuating Soil Moisture Conditions.

Nitrous oxide (N₂O) is a greenhouse gas that is released from both aerobic nitrification and anaerobic denitrification processes. Soil moisture content is a key controller of the biochemical pathways leading to N₂O emission, causing a switch between nitrification and denitrification processes. Earthworms increase N₂O emissions from soil, but how earthworm activities are affected with fluctuations in soil moisture and the impact on soil N₂O emission is unknown. The objectives of this study were to (1) evaluate the soil moisture effects on earthworm activities, and (2) link these effects to earthworm-induced N₂O emissions under three soil moisture regimes (constant aerobic, constant anaerobic and fluctuating anaerobic-aerobic conditions). During a two month mesocosm study, earthworms from endogeic and anecic functional groups were kept in PVC tubes (10 cm diam. by 20 cm tall)  with 5 replicates of each soil moisture regime. In each cycle, earthworm growth rate was measured and N₂O flux were quantified every 1-2 d. From the preliminary results, N₂O was emitted at a relatively constant rate from soil under constant anaerobic conditions, with and without earthworms. Nevertheless, earthworms significantly enhanced the N₂O emission rate in the soil that was constantly aerobic. In the fluctuating soil moisture regime, soil without earthworms had higher N₂O rate when the soil was wet, while the soil with earthworms had a high N₂O emission rate even when the soil was dry. Our results will relate earthworms and N₂O emissions under constant and fluctuating soil moisture conditions, which provide insights into N₂O emission in riparian areas.