Warming Shapes nirS- and nosZ-Type Denitrifier Communities and Stimulates N₂O Emission in Acidic Paddy Soil

Warming strongly stimulates soil nitrous oxide (N₂O) emission, contributing to the global warming trend. Submerged paddy soils exhibit huge N₂O emission potential; however, the N₂O emission pathway and underlying mechanisms for warming are not clearly understood. We conducted an incubation experiment using ¹⁵N to investigate the dynamics of N₂O emission at controlled temperatures (5, 15, 25, and 35°C) in 125% water-filled pore space. The community structures of nitrifiers and denitrifiers were determined via high-throughput sequencing of functional genes. Our results showed that elevated temperature sharply enhanced soil N₂O emission from submerged paddy soil. Denitrification was the main contributor, accounting for more than 90% of total N₂O emission at all treatment temperatures. N₂O flux was coordinatively regulated by nirK-, nirS-, and nosZ-containing denitrifiers but not ammonia-oxidizing archaea or ammonia-oxidizing bacteria. The nirS-containing denitrifiers were more sensitive to temperature shifts, especially at a lower temperature range (5 to 25°C), and showed a stronger correlation with N₂O flux than that of nirK-containing denitrifiers. In contrast, nosZ-containing denitrifiers exhibited substantial variation at higher temperatures (15 to 35°C), thereby playing an important role in N₂O consumption. Certain taxa of nirS- and nosZ-containing denitrifiers regulated N₂O flux, including nirS-containing denitrifiers affiliated with Rhodanobacter and Cupriavidus as well as nosZ-containing denitrifiers affiliated with Azoarcus and Azospirillum. Together, these findings suggest that elevated temperature can significantly increase N₂O emission from denitrification in submerged paddy soils by shifting the overall community structures and enriching some indigenous taxa of nirS- and nosZ-containing denitrifiers. IMPORTANCE The interdependence between global warming and greenhouse gas N₂O has always been the hot spot. However, information on factors contributing to N₂O and temperature-dependent community structure changes is scarce. This study demonstrated high-temperature-induced N₂O emission from submerged paddy soils, mainly via stimulating denitrification. Further, we speculate that key functional denitrifiers drive N₂O emission. This study showed that denitrifiers were more sensitive to temperature rise than nitrifiers, and the temperature sensitivity differed among denitrifier communities. N₂O-consuming denitrifiers (nosZ-containing denitrifiers) were more sensitive at a higher temperature range than N₂O-producing denitrifiers (nirS-containing denitrifiers). This study's findings help predict N₂O fluxes under different degrees of warming and develop strategies to mitigate N₂O emissions from paddy fields based on microbial community regulation.