Nitrogen Supply Regulates Stomatal Traits and Reduces Diurnal Transpiration Rate in Potato Under Non‐Limiting Water Conditions

ABSTRACT Nitrogen (N) supply plays a critical role in influencing the onset of drought thresholds, yet the effects of N on stomatal characteristics and transpiration, both diurnal and nocturnal, remain inadequately understood. To elucidate the relationship between transpiration rate and stomatal morphology, this study investigated the effects of four distinct levels of N supply (N0, N0.1, N0.2, and N0.4) on stomatal density (SD) and morphology across both adaxial and abaxial leaf surfaces, alongside their impact on diurnal ( E d ) and nocturnal ( E n ) transpiration rates in potato plants. The findings indicate that SD decreases with increasing N supply on both leaf surfaces. Furthermore, stomatal apertures were consistently larger on the abaxial surface compared to the adaxial surface across all N supply treatments. While E n remained largely unaffected by variations in N supply, E d exhibited a non‐linear decrease as N supply increased, reaching its minimum value at the N0.2 level. This reduction in E d , which plateaued at N0.2, is likely associated with the larger stomatal aperture on the abaxial surface at the highest N supply level (N0.4) compared to the other treatments. Overall, the results suggest that N supply primarily reduces E d by decreasing SD, while also maintaining a larger stomatal aperture on the abaxial surface under high N conditions to optimize the balance between CO 2 uptake and water loss. The findings can provide valuable insights into the role of N supply for sustainable crop management, particularly in optimizing water‐use efficiency.