Objective This study aimed to explore the synergistic effects of different mycorrhizal fungi under salt stress and their regulatory mechanisms on plant physiological responses, providing a potential strategy to enhance their stress resistance.

Method A pot experiment was conducted under short-term stress induced by 0.8% NaCl. Seedlings of Juglans regia 'Yanyuanzao' were individually or co-inoculated with Funneliformis mosseae and Piriformospora indica, with a non-inoculated group serving as the control. The effects of single and combined inoculation on the growth and physiological characteristics of walnut seedlings under salt stress were evaluated.

Result Salt stress inhibited the growth of walnut seedlings, reducing biomass and causing leaf damage, but mycorrhizal fungal inoculation significantly alleviated these stress symptoms, reducing the biomass of non-inoculated treatments by up to 44.87% compared to the inoculated ones. Inoculation with mycorrhizal fungi significantly alleviated these stress symptoms. Under salt stress, mycorrhizal fungi significantly increased the net photosynthetic rate of walnut seedlings, with an increase of 31.81% to 42.78%. The combined inoculation significantly increased the total chlorophyll content of walnut seedlings under salt stress, with an increase of 9.77% to 21.68%. F. mosseae specifically activated the activities of peroxidase (POD) and ascorbate peroxidase (APX), leading to a 20.26% reduction of in malondialdehyde (MDA) content. In contrast, P. indica primarily regulated hormone levels. increasing abscisic acid (ABA) and auxin (IAA) contents by 36.56% and 32.81%, respectively.

Conclusion Walnut is inherently sensitive to salt stress, which severely inhibits its growth and development. However, inoculation with mycorrhizal fungi significantly improves the salt tolerance of walnut seedlings. Comparative analysis shows that F. mosseae promotes antioxidant enzyme activity, P. indica promotes hormonal regulation, and their combined inoculation exerts a significant synergistic effect under salt stress, enabling the seedlings to maintain growth and physiological stability during prolonged salt stress.