The impact of precipitation on N2O emissions during the freeze-thaw cycle in a typical grassland in Inner Mongolia

Abstract

Approximately 78 % of China’s grasslands are located north of 30° N latitude where seasonal freeze-thaw processes are prevalent, and the freeze-thaw cycle plays a key role in regulating N₂O emissions. Climate factors, particularly winter precipitation influences soil water dynamics, thermal processes, and nitrogen cycling. Here, we hypothesize that winter precipitation significantly affects N₂O emissions by altering soil water content and nitrogen cycling processes during the freeze-thaw cycle. In this study, nine measurements of N₂O fluxes were conducted during the freeze-thaw periods of 2018, 2021, and 2023, along with soil water and thermal monitoring, across three grazing treatments in the Inner Mongolia Grassland: ungrazed since 1979 (UG79), ungrazed since 1999 (UG99), and continuously grazed (CG). Results show that winter precipitation was very associated with the hydrologic year, highest in 2021 (wet year), followed by 2023 (average year), and lowest in 2018 (drought year). High pulse N₂O emissions occurred only in the drought year, while in the wet year, deeper soil (20–50 cm) had significantly higher N₂O concentrations, but surface N₂O fluxes were lower, even a negative value as a sink. Structural equation modeling indicated that cumulative winter precipitation, soil nitrogen availability (especially NH₄⁺-N), and surface soil moisture were key factors influencing N₂O emissions. Increased winter precipitation enhanced soil moisture and deep soil N₂O concentrations but reduced permeability, promoting denitrification and lowering emissions. This indicates that winter precipitation affects soil N₂O fluxes and concentrations through multiple mechanisms. To improve N₂O emission predictions, winter precipitation dynamics and soil ammonium nitrogen must be considered.