Accumulation of NO2− during periods of drying stimulates soil N2O emissions during subsequent rewetting

Abstract

SummaryRewetting of soil might contribute considerably to the annual production of nitrous oxide (N2O) in ecosystems subjected to long dry periods. Therefore, it is crucial to elucidate the most important factors responsible for large pulses of N2O with rewetting. In this study, we carried out a series of rewetting experiments with soil samples collected from upland and riparian forest, grassland and arable land. We analysed the dynamics of ammonium (NH4+), nitrite (NO2−), nitrate (NO3−) and dissolved organic matter (DOM) of air‐dried soil samples after rewetting. We also analysed the effects of sterilization of soil samples by γ‐irradiation on N2O production with rewetting. Furthermore, we explored the effects of rewetting and sterilization on the isotopic composition of N2O in the different soil samples. The grassland soil produced the largest amount of N2O (64.1 μg N kg−1) in 1 hour on rewetting, followed by upland forest soil, whereas it was least for soils from riparian forest and arable land. Gamma irradiation, however, decreased soil N2O production from forest soil samples by 30–90% after rewetting, but increased N2O production in grassland and arable land soils three‐fold and two‐fold, respectively. Correlation analysis revealed that NO2− concentration in the soil samples at the time of rewetting was the most relevant factor that explained soil N2O production after rewetting. Furthermore, the addition of NO2− before rewetting increased N2O production during rewetting more than with additions of NO3− and NH4+ in all soil samples. The 15N site preference values of N2O produced after rewetting were close to 0‰, indicating a denitrification‐related production process according to the classical view. However, additional abiotic processes responsible for soil N2O production during rewetting cannot be excluded.Highlights Mechanisms responsible for large N2O production during rewetting of soil are not well understood. Nitrite content in dry soil was strongly correlated with N2O production after rewetting. The 15N site preference of the N2O produced was close to 0‰ after rewetting. Additional abiotic processes could have contributed to N2O formation from NO2−.