Divergent mechanisms govern N2O emissions from Qinghai-Tibet Plateau alpine meadows in freeze versus thaw periods

Abstract

Substantial nitrous oxide (N₂O) emissions from permafrost-affected regions could accelerate climate warming, given that N₂O exhibits approximately 300 times greater radiative forcing potential than carbon dioxide. Pronounced differences exist in N₂O emissions between freeze and thaw periods (FP and TP), but the mechanisms by which environmental factors regulate the production and emission of N₂O during these two periods have not been thoroughly examined. We therefore combined static chamber gas chromatography, in-situ soil temperature (ST) and moisture (SM) monitoring, and 16S rRNA sequencing to investigate seasonal N₂O variations in the Qinghai-Tibet Plateau (QTP) alpine meadow ecosystem, and assess the relative contributions of environmental and microbial drivers. Our findings indicate that N₂O fluxes (−3.15 to 6.10 μg m⁻² h⁻¹) fluctuated between weak sources and sinks, peaking during FP, particularly at its late stage with initial surface soil thawing. Soil properties affect N₂O emissions by regulating denitrification processes and altering microbial community diversity. During the FP, ST fluctuations control N₂O release by modifying mineral nutrient availability. During TP, soil texture modulates denitrification-driven N₂O production through its effect on SM. Spring N₂O pulses likely originate from microbial reactivation in thawed soil. N₂O accumulated in frozen soil may gradually release during vertical profile thawing. On the QTP, a warmer and wetter climate scenario may alter N₂O emissions by modifying the duration of the FP and TP and phase-specific hydrothermal allocation. This study provides mechanistic insights for predicting climate change impacts on N₂O flux in fragile alpine meadow ecosystems.