Inundation mitigates the nitrogen-induced increase in soil nitrous oxide emissions in estuarine and coastal wetlands

Nitrogen enrichment and sea-level rise are two critical drivers affecting estuarine and coastal wetland ecosystems globally. However, the effects of these drivers on soil nitrous oxide (N 2 O) production, consumption, and resulting ultimate emissions remain poorly understood. In this study, nitrogen input (+N treatment), increased inundation (+I treatment), and their combination (+N+I treatment) were simulated in situ using a weir device to explore the individual and interactive effects of enhanced nitrogen loading and sea-level rise on soil N 2 O dynamics. Our results showed that nitrogen input (+N treatment) significantly increased soil N 2 O emission (82.9%), primarily by stimulating gross N 2 O production. In contrast, the inundation increases alone (+I treatment) did not alter soil N 2 O production and consumption process dynamics. The Combined treatment of increased nitrogen input and inundation (+N+I treatment) dramatically promoted soil gross N 2 O production (85.3%). However, an elevated proportion of N 2 O consumption mitigates its effect on N 2 O emissions. This implies that increased inundation resulting from the sea level rise may counteract nitrogen-stimulated soil N 2 O emissions. The contents of soil carbon and nitrogen substrate (e.g., DOC and NH 4 + ), along with the gene abundances (e.g., nosZ) involved in N 2 O production and consumption, were the pivotal factors in mediating the changes in N 2 O dynamics under various treatments. Overall, our findings highlighted the importance of increased inundation caused by sea-level rise in alleviating N 2 O emissions under high nitrogen conditions, yet widely overlooked.