Extreme Rainfall Amplified the Stimulatory Effects of Soil Carbon Availability on N 2 O Emissions

Ongoing climate change is predicted to increase the frequency and intensity of extreme rainfall, which will dramatically alter soil nitrous oxide (N 2 O) emissions, especially changes in soil organic carbon (SOC) due to anthropogenic management. However, our ability to predict this effect is limited owing to a dearth of research. Therefore, we selected two croplands in Northeast China with the same quantity but contrasting availability of SOC to explore the in situ dynamics of N 2 O fluxes and N‐cycling microbes through 2‐year field experiment and N 2 O production pathways by laboratory 15 N‐tracing experiment. In a normal rainfall year, the croplands with high (HCA) and low (LCA) SOC availability emitted 0.66 and 0.25 kg N 2 O‐N ha −1 without N‐fertilization and 2.03 and 1.51 kg N 2 O‐N ha −1 with N‐fertilization, respectively. In a record‐breaking wet year, multiple heavy rainfall events caused water supersaturation in the low‐lying HCA cropland over 2 months. Consequently, the background N 2 O emissions increased by 508% compared with the normal rainfall year, and the N‐induced N 2 O emission factor increased from 0.77% to 2.24%. Soil dissolved organic carbon (DOC) was identified as the primary driver of larger N 2 O fluxes from HCA cropland which facilitated denitrification by fueling nirS ‐ and nirK ‐denitrifiers metabolism. Furthermore, a greater N substrate supply via a faster mineralization‐nitrification coupling process promoted the contribution of autotrophic nitrification to N 2 O in HCA cropland. The N 2 O pulses from HCA soils during the waterlogging period were derived from stimulated denitrification, which dominated N 2 O production (> 90%). Simultaneously, C availability enhanced and nitrate was produced via archaeal nitrification, leading to an increased nirS / nosZII ratio that fostered N 2 O production through incomplete denitrification. Overall, our findings highlight the importance of avoiding the amendment of exogenous organic materials with high C lability, particularly under climate extremes, to eliminate the potential positive feedback of SOC management on climate change by inducing N 2 O emissions.