Asynchronous recovery of canonical ammonia oxidizers and comammox drives post-drought N2O emissions in contrasting soils.

Intensifying drought regimes driven by global climate change pose a severe threat to soil nitrogen cycling stability. While the metabolic responses of microbes to stress are documented, the mechanisms linking the differential resilience of nitrifying guilds to post-drought nitrous oxide (N2O) pulses remain elusive. Here, we investigated the recovery dynamics of ammonia-oxidizing archaea (AOA), bacteria (AOB), and comammox Nitrospira alongside temporal N2O emission pulses in contrasting acidic and alkaline soils following common drought and extreme drought. Treatment effects and community structural divergence were evaluated using permutational multivariate analysis of variance (PERMANOVA). Post-drought response patterns differed among guilds: AOA and AOB exhibited marked population fluctuations, signaling a resilience-based recovery, whereas comammox Nitrospira demonstrated greater abundance stability, maintaining stable abundance in both soils throughout the 60-day incubation. Community reassembly was primarily governed by soil pH, which acted as a divergent environmental filter; specifically, acidic conditions favored the dominance of AOA and comammox, whereas alkaline conditions selectively promoted AOB proliferation. Critically, N2O emissions correlated with recovery patterns among the specific nitrifier guilds. Random forest modeling demonstrated that comammox was the primary driver of emissions during the rapid "early recovery" phase of rewetting, while the delayed resurgence of AOA and AOB sustained N2O production in the later stages, revealing the asynchronous recovery of these guilds modulated the temporal duration of nitrification-derived N2O fluxes. This study highlights how the temporal niche differentiation of nitrifiers regulates the magnitude and duration of nitrogen losses following extreme drought events.