Effects of Salt Stress on Physiological Characteristics of Tulip (Tulipa gesneriana L.) Bulb Germination

China has a vast area of saline-alkali land, and cultivating salt-tolerant plant varieties is crucial for improving the saline-alkali environment. Tulips are known to have a certain level of salt tolerance. This study aimed to investigate the physiological responses of different tulip cultivars to salt stress during bulb germination. Four conventional tulip cultivars: ‘Candy Apple Delight’, ‘Orange Emperor’, ‘Salmon Impression’ and ‘Red Impression’, were chosen as research materials. After bulb germinating, we were subjected to salt stress using 0.4 mol L^–1 NaCl solution. Phenotypic observations of roots and leaves were conducted on the 0, 3, 6, 9, 12, 15, 18, and 21 days of treatment. The roots of the treatment group and the control group were collected to analyze peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), Na⁺/K⁺-ATPase activities, and hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and proline (Pro) levels. The results show: (1) Salt stress had the most severe effect on the aboveground part of ‘Orange Emperor’, the greatest impact on the underground part of ‘Candy Apple Delight’, and the least impact on ‘Salmon Impression’ and ‘Red Impression’; (2) under salt stress, the POD activity of tulip cultivars showed a consistent variation trend. Both ‘Candy Apple Delight’ and ‘Salmon Impression’ exhibited an initial increase followed by a decrease in SOD, CAT activities, and MDA content. On the other hand, the trend for H₂O₂, Pro, and Na⁺/K⁺-ATPase activity was ‘decreasing—increasing—decreasing’. The H₂O₂, MDA, Pro, and Na⁺/K⁺-ATPase activities of ‘Orange Emperor’ were in line with the variation trends of H₂O₂ and MDA in ‘Red Impression’, which also followed a ‘decreasing—increasing—decreasing’ pattern. The SOD and CAT activity of ‘Orange Emperor’ and ‘Red Impression’, as well as Pro and Na⁺/K⁺-ATPase Activity with ‘Red Impression’, showed a similar changing trend of initial increase followed by a decrease. However, the response time to salt stress varied among different cultivars and indexes. (3) Principal component analysis revealed that the salt tolerance of the four tulip cultivars was ranked as ‘Red Impression’ > ‘Salmon Impression’ > ‘Candy Apple Delight’ > ‘Orange Emperor’, and the 6th of salt stress was the most sensitive period of tulip cultivars to salt stress. In conclusion, all tulip cultivars have a certain level of adaptability to salt stress, but there are variations among the different cultivars. The ability to adapt to salt stress can be enhanced through the coordination of various physiological indicators. This study elucidated the physiological mechanism of salt tolerance in different tulip cultivars, providing valuable insights for tulip cultivation in saline-alkali soil and contributing to further scientific research on tulips.