| To investigate the effects of drought and salinity stress on water productivity, photosynthetic pigments, and elemental concentrations in peppermint (Mentha piperita L.) under melatonin application, a factorial experiment with three replications was conducted in Torbat-e Jam in 2024. The treatments included three levels of salinity (0, 50, and 100 mM NaCl), three levels of drought stress (100, 75, and 50% of water requirement), and two levels of foliar-applied melatonin (0 and 100 µM). The results indicated that increasing drought stress significantly increased water productivity by 15% and 40%, iron concentration by 6.04% and 68.45%, zinc concentration by 15.38% and 192.3%, sodium concentration by 26.41% and 63%, potassium concentration by 12% and 14.08%, and the Na⁺/K⁺ ratio by 30.55% and 41.66%, respectively. In contrast, chlorophyll a decreased by 9.64% and 25.35%, chlorophyll b by 9.74% and 22.07%, total chlorophyll by 9.67% and 24.19%, and carotenoids by 8.98% and 26.96%, respectively. Increasing drought stress initially increased the essential oil percentage by 20.25%, followed by a reduction of 27.85% at higher stress levels. Salinity stress reduced water productivity by 34.70% and 52.61%, iron concentration by 21.27% and 28%, zinc concentration by 87.11% and 83.65%, chlorophyll a by 7.71% and 32.63%, chlorophyll b by 11.32% and 28.93%, total chlorophyll by 9.21% and 31.23%, carotenoids by 14.89% and 35.10%, and the essential oil percentage by 25.49% and 47.06%, respectively. In contrast, sodium concentration increased from 10.40 to 26.90 and 152.11 mg/g, while potassium concentration increased by 3.3% and then decreased by 3.48%, and the Na⁺/K⁺ ratio increased from 0.053 to 0.15 and 1.13, respectively. Foliar application of melatonin improved water productivity, zinc concentration, potassium concentration, chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids by 17.81%, 31.57%, 33.06%, 5.83%, 6%, 5.88%, and 8%, respectively, while reducing iron concentration, sodium concentration, and the Na⁺/K⁺ ratio by 14.71%, 15.44%, and 28.84%, respectively. Overall, the findings demonstrate the effectiveness of melatonin in mitigating the adverse effects of salinity and drought stress on peppermint growth, physiological traits, and mineral nutrition. |