Wheat Plants Reduce N₂O Emissions from Upland Soil Subject to Transient and Permanent Waterlogging

Climate change is expected to increase the frequency of extreme soil moisture events, such as winter waterlogging followed by spring drought, particularly in temperate regions of Europe, North America and Northeast China. While N₂O emissions from paddy soils under waterlogging and subsequent drainage have been widely studied, knowledge of upland arable soils under wheat cultivation remains limited. We hypothesized that: (1) in upland soils, combined waterlogging and drought reduces N₂O emissions compared to continuous waterlogging, and (2) plant presence mitigates soil nitrate accumulation and N₂O emissions across different moisture regimes. A greenhouse experiment was conducted using intact upland soil cores with and without wheat under four moisture treatments: control (60% water-holding capacity, WHC), drought (30% WHC), waterlogging, and waterlogging followed by drought. Daily and cumulative N₂O fluxes, soil mineral nitrogen (NH₄⁺-002DN and NO₃⁻-N), and total nitrogen uptake by wheat shoots were measured. Prolonged waterlogging resulted in the highest cumulative N₂O emissions, whereas the transition from waterlogging to drought triggered a sharp but transient N₂O peak, particularly in soils without plants. Wheat presence consistently reduced N₂O emissions, likely through nitrate uptake, which limited substrate availability for incomplete denitrification. Moisture regimes strongly affected nitrate dynamics, with drought promoting nitrate accumulation and waterlogging enhancing nitrate loss. These findings highlight the vulnerability of upland soils in regions prone to seasonal moisture extremes. Effective management of soil moisture and nitrogen, including the promotion of plant growth, is essential to mitigate N₂O emissions and improve nitrogen use efficiency under future climate scenarios.