Abstract: Understanding the physiological responses of Ping’ou hybrid hazelnut to salt stress and the variations of salt tolerance of different varieties can provide scientific reference for the breeding of salt-tolerant varieties and their rational utilization in saline-alkali soil. The seedlings of three Ping’ou hybrid hazelnut varieties (Dawei, Liaozhen 7, and Yuzhui) were treated with control, mild, moderate and severe salt stress (0, 50, 100, and 200 mmol·L^-1 NaCl, respectively) in a pot experiment. Leaf physiological indices related to salt tolerance were measured. The results showed that salt stress did not affect leaf relative water content of Dawei, while significantly reduced that of Liaozhen 7 and Yuzhui by 12.5% and 27.9%, respectively, under severe salt stress. With increasing salt stress, leaf soluble sugar and soluble protein increased first and then decreased. The proline content increased continuously, with an increment of 19.6%, 35.3%, and 96.9% under mild, moderate, and severe stress, respectively. The relative electrical conductivity, malondialdehyde and catalase activity in leaves increased with increasing salt stress. The superoxide dismutase activity in leaves increased first and then decreased, while peroxidase activity decreased first and then increased. With increasing salt stress, leaf Na⁺ and Cl^- contents increased. The K⁺ content increased first and then decreased, and significantly increased by 43.6% and decreased by 28.3% under the moderate and severe stress, respectively. The K⁺/Na⁺ ratio decreased, with a significant decrease of 69.5% under severe stress. Our results suggested that Ping’ou hybrid hazelnut positively responded to mild and moderate salt stress through accumulating leaf osmotic adjustment substances, improving antioxidant enzyme activity, maintaining ion balance, which could help to reduce the damage of reactive oxygen under stress and protect the structure and function of membrane system. Plants suffered from severe stress that exceeded the threshold of normal physiological activities of Ping’ou hybrid hazelnut. Liaozhen 7 showed the strongest tolerance to salt stress through physiological regulation, followed by Yuzhui and Dawei.

Key words: salt stress, physiological characteristics, salt tolerance evaluation, Ping’ou hybrid hazelnut.