PRI and DI under moderately and severely watering levels had similar WUE and significantly lower plant N uptake compared to well-watered treatment. PRI plants had the highest δ13C indicating the better control of stomata compared to DI plants.. PRI and DI plants had significantly higher plant δ15N than FI treatment, indicating a greater contribution of N from soil organic N pool to N uptake. Sustaining high water levels in PRI wet soil zone is critical for improving N uptake.