To investigate the effects of nitrogen addition on water use efficiency and related enzyme activities of P. massoniana seedlings under continuous drought and re-watering, and to provide reference for exploring whether nitrogen addition improves drought resistance of P. massoniana.

One-year-old P. massoniana seedlings were used as experimental materials, and a nitrogen application group (N) and a control group (CK, no nitrogen fertilizer applied) were set up. Continuous drought and re-watering experiments were conducted through potted plants. Samples were collected at 0, 20, 40, and 60 days during continuous drought, as well as two days after re-watering. Soil water content, physiological and biochemical indices, and water consumption were measured for drought resistance evaluation.

1) The nitrogen application group increased soil moisture content, stem water potential, amino acid content, and water consumption of seedlings during the severe extreme drought stage (20-60 days), while reducing soluble protein, superoxide anion, and malondialdehyde content during the extreme drought stage (40-60 days); 2) During 40-60 days of drought, the nitrogen application group showed a significant increase in amino acid, proline content, and CAT activity; 3) After re-watering, the soluble protein, superoxide anion, and malondialdehyde content, as well as the activities of superoxide dismutase and catalase, were significantly reduced in the nitrogen application group, while the control group maintained high levels, indicating weak recovery ability after drought; 4) The comprehensive evaluation of drought resistance was conducted on physiological and biochemical indicators using the membership function method. The results showed that during the extreme drought stage (40-60 days), the nitrogen application group exhibited strong drought resistance.

Nitrogen application can improve soil water retention during drought periods, increase the content of osmoregulatory substances in P. massoniana seedlings, and enhance antioxidant enzyme activity, thereby reducing cell dehydration and mitigating oxidative damage to seedlings, thus improving their drought resistance and post-drought recovery ability under drought stress.