Drought-induced nitrous oxide flux dynamics in an enclosed tropical forest

El Niño-La Niña cycles strongly influence dry and wet seasons in the tropics and consequently nitrous oxide (N₂O) emissions from tropical rainforest soils. We monitored whole-system and soil chamber N₂O fluxes during 5-month-long droughts in the Biosphere 2 tropical forest to determine how rainfall changes N₂O production. A consistent pattern of N₂O flux changes during drought and subsequent wetting emerged from our experiments. Soil surface drying during the first days of drought, presumably increased gas transport out of the soil, which increased N₂O fluxes. Subsequent drying caused an exponential decrease in whole-system (4.0±0.1% day^-1) and soil chamber N₂O flux (8.9±0.8% day^-1; south chamber; and 13.7±1.1% day^-1; north chamber), which was highly correlated with soil moisture content. Soil air N₂O concentration ([N₂O]) and flux measurements revealed that surface N₂O production persisted during drought. The first rainfall after drought triggered a N₂O pulse, which amounted to 25% of drought-associated reduction in N₂O flux and 1.3±0.4% of annual N₂O emissions. Physical displacement of soil air by water and soil chemistry changes during drought could not account for the observed N₂O pulse. We contend that osmotic stress on the microbial biomass must have supplied the N source for pulse N₂O, which was produced at the litter-soil interface. After the pulse, N₂O fluxes were consistently 90% of predrought values. Nitrate change rate, nutrient, [N₂O], and flux analyses suggested that nitrifiers dominated N₂O production during the pulse and denitrifiers during wet conditions. N₂O flux measurements in Biosphere 2, especially during the N₂O pulse, demonstrate that large-scale integration methods, such as flux towers, are essential for improving ecosystem N₂O flux estimates.