Moisture-microbial interaction amplifies N2O emission hot moments under deepened snow in grasslands

Freeze-thaw periods contribute disproportionately to annual N₂O emissionsrepresenting a critical yet understudied component of its global budget. Understanding drivers of these hot moments and their sensitivity to climate change is essential, but their episodic nature and great spatiotemporal variability pose substantial challenges. Combining cross-ecoregion soil core incubations with in-situ automated measurements, we explored snow regime shift effects on N₂O emissions. Our findings revealed ~50-day pulse emissions during freeze-thaw periods, accounting for over 50% of annual fluxes, increasing nonlinearly with snow depth. Emissions were regulated by water-filled pore space (WFPS) thresholds: below 43%, soil moisture dominated; at 43%–66%, moisture and microbial attributes jointly triggered emissions; above 66%, microbial attributes, particularly N enzyme kinetics, prevailed. Hotspots of freeze-thaw-induced emissions were linked to high root production and microbial activity in cold, humid grasslands. This hierarchical control of WFPS and microbial processes provides a framework for predicting the location and magnitude of freeze-thaw-induced N₂O pulses, improving N₂O accounting and informing mitigation strategies.