Extreme Rainfall Amplified the Stimulatory Effects of Soil Carbon Availability on N<sub>2</sub>O Emissions
Zengming Chen, Nan Zhang, Ye Li, Shiqi Xu, Yulian Liu, Shujie Miao, Weixin Ding
Abstract
ABSTRACT 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.