Freeze-thaw-induced greenhouse gas emissions from a Mollisol agroecosystem: Microbial and edaphic regulation under long-term agricultural management

Freeze-thaw events contribute substantially to annual soil greenhouse gas (GHG) emissions. However, it remains unclear how soil properties and microbial characteristics, altered by long-term agricultural management, individually or interactively regulate GHG emissions. To address this gap, we quantified CO 2 , CH 4 , and N 2 O fluxes through field monitoring during seasonal freeze-thaw periods in Mollisol farmland of Northeast China. Results demonstrated that CO 2 and CH 4 emissions were higher during the thawing period than the freezing period, with CH 4 emission increasing by 266%; overall emissions of both GHGs were greater in high-fertility soils. While N 2 O exclusively peaked during the thawing period, with its mean peak flux 1.68 times higher in high-fertility soils than in low-fertility soils. These emission patterns were further amplified under maize monoculture compared to maize-soybean and maize-fallow rotation systems. During the freeze-thaw process, GHG fluxes were primarily driven by variations in soil temperature, moisture, and aggregate stability. The alleviation of resource-microbe carbon:nitrogen (C:N) imbalance during the thawing period likely stimulated pulses of CO 2 , CH 4 , and N 2 O emissions. This effect was more pronounced in soils with initial properties characterized by lower C:N ratio, greater available C and N, and stronger microbial stress tolerance (indicated by higher fungal: bacterial and gram-positive: gram-negative ratios). These mechanisms underpin the greater cumulative GHG emissions observed in high-fertility soils and continuous monocropping systems. Collectively, our findings suggest that long-term fertilization and maize monoculture amplify freeze-thaw-induced GHG emissions via specific edaphic-microbial properties, providing field evidence for mitigating non-growing season climate impacts through optimized management.