Magnitude and Drivers of Nitrous Oxide Emission Pulses Over the Seasonal Transition: A Synthesis

Abstract

The magnitude of nitrous oxide (N ₂ O) emission pulses during the winter‐to‐spring seasonal transition (ST) can exceed summer peaks, but this component remains poorly constrained in the global N ₂ O budget. Here, we conducted a synthesis of 182 observations without fertilizer applications using machine‐learning, hierarchical mixed‐effects models, and structural equation modeling to compare ST‐N ₂ O pulse magnitude and identify its dominant drivers. The average rate of ST‐N ₂ O pulse was 63.2 μg m ⁻²  hr ⁻¹ , approximately 3.5 times higher than that during the growing season. Moreover, the average ST‐N ₂ O pulse was 108.2 mg m ⁻² in non‐croplands, which is 2.4 times greater than that in croplands without nitrogen fertilizer (46 mg m ⁻² ). ST‐N ₂ O pulse was influenced by the microbial vernal dam (MVD, defined as the seasonal release of microbial biomass nitrogen), microbial biomass carbon, soil respiration rate, and ammonium content. Soil MVD emerged as the dominant driver of ST‐N ₂ O pulse across ecosystem types, accounting for 21% of the observed variation. Cumulative ST‐N ₂ O pulses accounted for 2.9% of the nitrogen derived from MVD. These results highlight a ubiquitous hot moment in terrestrial N ₂ O emissions and provide a mechanistic basis for improving annual N ₂ O budgets and model parameterization.