Impact of extreme precipitation and water table change on N₂O fluxes in a bio-energy poplar plantation

Abstract. A large fraction of the West European landscape is used for intensive agriculture. Several of these countries have very high nitrous oxide (N₂O) emissions, because of substantial use of fertilizers and high rates of atmospheric nitrogen deposition. N₂O production in soils is controlled by water-filled pore space (WFPS) and substrate availability (NO₃). Here we show that extreme precipitation (80 mm rainfall in 48 h) after a long dry period, led to a week-long peak in N₂O emissions (up to about 2200 μg N₂O-N m⁻² h⁻¹). In the first four of these peak emission days, N₂O fluxes showed a pronounced diurnal pattern correlated to daytime increase in temperature and wind speed. It is possible that N₂O was transported through the transpiration stream of the poplar trees and emitted through the stomates. However, during the following three high emission days, N₂O emission was fairly stable with no pronounced diurnal trend, and was correlated with wind speed and WFPS (at 20 and 40 cm depth) but no longer with soil temperature. We hypothesized that wind speed facilitated N₂O emission from the soil to the atmosphere through a significant pressure-pumping. Successive rainfall events and similar WFPS after this first intense precipitation did not lead to N₂O emissions of the same magnitude. These findings suggest that climate change-induced modification in precipitation patterns may lead to high N₂O emission pulses from soil, such that sparser and more extreme rainfall events after longer dry periods could lead to peak N₂O emissions. The cumulative effects of more variable climate on annual N₂O emission are still largely uncertain and need further investigation.