Abstract: 【Objective】To investigate the effects of mixed saline-alkali stress on the growth and physiological metabolism of rice seedlings.【Methods】Eight japonica rice varieties were used as experimental materials. Three gradients of mixed saline-alkali stress were set with salt-alkali ratios of 7∶3（SA1）,5∶5（SA2） and 3∶7（SA3）,with distilled water treatment as the control（CK）. After 7 days of mixed saline-alkali stress,growth and physiological indices of rice seedlings were measured.【Results】Compared to the control（CK）,mixed saline-alkali stress significantly increased the rate of withered leaves by 57.49%-98.43%,and significantly reduced chlorophyll content by 49.63%-79.01%,water content of leaves by 3.75-30.90 percentage points,water content of roots by 3.63-14.31 percentage points,total root length by 14.55%-56.81%,and root tip numbers by 23.28%-71.71%（P<0.05）;the contents of osmoregulatory substances,Na⁺,and reactive oxygen species（ROS） in rice seedlings significantly increased（P<0.05）,while K⁺ content significantly decreased（P<0.05） under all treatments. Saline-sensitive varieties exhibited a higher degree of inhibition in growth indices,lower contents of osmoregulatory substances and K⁺,and higher contents of ROS and Na⁺ under mixed saline-alkali stress compared to salt-tolerant varieties.【Conclusion】The inhibition of rice seedling growth under mixed saline-alkali stress is the result of combined osmotic stress,ion toxicity,and high pH stress,with root growth being more severely affected;elevated pH value aggravates ion toxicity and high pH-induced stress,disrupts the osmoregulatory system,causes multiple physiological and metabolic disorders,and ultimately inhibits seedling growth.

Key words: Mixed saline-alkali stress, Rice, Seedling, Root system, Physiological metabolism