Nitrogen addition regulates post-drought N2O emissions by reshaping the resilience of canonical and complete ammonia oxidizers in subtropical red soil.

The resilience of ammonia-oxidizing guilds can regulate nitrification after drought, yet how nitrogen input modifies guild-specific recovery and post-drought nitrous oxide (N2O) emissions remains unclear. We conducted a 90-day cultivation experiment with subtropical acidic red soil, including 30 days of drought stress followed by 60 days of rewetting recovery. Treatments included a constant-moisture control (CK), post-drought recovery without nitrogen addition (N0), low nitrogen addition (NL, 20 mg N kg-1), and high nitrogen addition (NH, 100 mg N kg-1). This study aimed to determine how nitrogen input regulates guild-specific nitrifier resilience and post-drought N2O emissions by monitoring N2O fluxes, soil physicochemical properties, and the abundance and diversity of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and complete ammonia oxidizers (comammox). Nitrogen input markedly increased post-drought N2O emissions, with 28-day cumulative emissions following the order NH (20.08 μg N2O-N g-1) > NL (14.71 μg N2O-N g-1) > N0 (10.72 μg N2O-N g-1) > CK (1.43 μg N2O-N g-1). AOA and comammox showed greater drought tolerance than AOB, whereas AOB recovered more strongly under high nitrogen input. Resilience indices further showed that low nitrogen addition favored the recovery of AOA and comammox, while high nitrogen addition promoted AOB recovery. Mantel analysis identified electrical conductivity (EC), microbial biomass carbon (MBC), and dissolved organic carbon (DOC) as important soil drivers of ammonia-oxidizer community shifts. Random forest analysis showed that comammox α-diversity resilience, AOB α-diversity resilience, and AOB abundance resilience were the strongest microbial predictors of post-drought N2O emissions. These findings demonstrate that nitrogen input regulates post-drought N2O emissions by reshaping soil recovery and guild-specific nitrifier resilience, rather than by increasing mineral nitrogen availability alone. This study highlights nitrifier resilience as a key microbial mechanism for predicting and managing N2O pulses under increasingly frequent drought-rewetting events.