Modulation of soil nitrous oxide emissions and nitrogen leaching by hillslope hydrological processes

Soil nitrous oxide (N₂O) emissions and nitrogen (N) leaching are key pathways for soil N loss in hillslope ecosystem, with potential implications for global warming and water body eutrophication. While soil N loss in hillslope ecosystem has been extensively studied, there is limited understanding of the spatiotemporal distribution patterns and factors driving soil N₂O emissions and N leaching from a hillslope hydrology perspective. This study investigated N concentrations in leachate and soil N₂O fluxes and their responses to soil hydrological factors on a tea plantation (TP) hillslope and a bamboo forest (BF) hillslope. Four distinct precipitation patterns-spring rainfall (SR), plum rain (PR), summer flood rain (SF), and drought period (DR)-were identified based on precipitation intensity, duration, and cumulative precipitation. Results showed that, soil N₂O flux and leachate N concentrations were 8.2 times and 18.0 times higher On TP hillslope compared to the BF hillslope. The greatest soil N₂O fluxes occurred during the PR period, while the lowest were observed during the DR period. Precipitation increased soil water content (SWC) and water-filled pore space, stimulating soil N cycling for N₂O production. Fertilization activities and precipitation led to peak N concentration in leachate during the SR period. Additionally, soil wetness index (SWI) shaped spatial patterns of SWC, resulting in distinct spatial patterns of N₂O emissions and nitrate leaching. Locations with higher SWI exhibited greater soil N₂O flux and higher nitrate concentrations in leachate. This study emphasizes the significant effect of soil hydrological processes on soil N₂O emissions and N leaching in hillslope ecosystems, providing valuable insights for N management in these environments.