Effects of Extreme Weather Events on Nitrous Oxide Emissions from Rice-Wheat Rotation Croplands.

Cropland ecosystems are significant emission sources of NO, but a limited number of studies have focused on the impact of extreme weather events on NO fluxes from cropland. This present study integrated field observations and model simulations to explore the responses of NO fluxes to extreme weather events in typical rice and wheat rotation croplands in the middle and lower reaches of the Yangtze River (MLRYR) in China. The findings revealed that the studied rice-wheat rotation cropland exhibited a net source of NO over the three-year monitoring period, with annual cumulative NO emissions ranging from 190.4 to 261.8 mg N m. NO emissions during the rice and wheat growing seasons accounted for 29% and 71% of the total yearly emissions, respectively. Extreme heat events led to a 23% to 32% increase in observed NO emissions from cropland. Observed NO emissions from irrigated rice fields during extreme precipitation events were 45% lower than those during extreme drought events. In contrast, extreme precipitation events raised observed NO emissions from rain-fed wheat fields by 36% compared to the multi-year average, while extreme drought events reduced NO emissions from wheat fields by 20%. Regional simulations indicated that annual cumulative NO emissions from croplands in the MLRYR are projected to increase from 207.8 mg N m under current climate to 303.4 mg N m in the future. Given the episodic nature and uncertainties associated with NO emissions from cropland, further validation is necessary for utilizing the model to explore the effects of extreme weather events on NO in cropland ecosystems.