Abstract:

To investigate the response of mycorrhizal fungi to the physiological mechanisms of walnut seedling roots under salt stress，Funneliformis mosseae and Piriformospora indica were selected as the fungal strains，and potted greenhouse seedlings of Juglans regia‘Yanyuanzao'were used as the plant material. Treatments included non-inoculation，single inoculation，and dual inoculation. Non-targeted metabolomics was employed to analyze the effects of the two mycorrhizal fungi and different inoculation methods on the content of plant endogenous hormones（jasmonic acid，salicylic acid，auxin，and abscisic acid）in the roots of walnut seedlings under short-term stress induced by 150 mmol · L^-1 NaCl solution. The results showed that both mycorrhizal fungi could colonize the roots of walnut seedlings，with no significant difference in the colonization rate between the inoculation treatments. Under salt stress，mycorrhizal fungi significantly affected the number of metabolites in the roots of walnut seedlings. Among these，inoculation with P. indica（single or dual inoculation）resulted in the highest number of differential metabolites，with 505 and 527 species，respectively. Enrichment analysis of metabolic pathways revealed that under salt stress，F. mosseae influenced nitrogen metabolism and glutathione metabolism，P. indica activated the pentose phosphate pathway and pantothenate biosynthesis pathway，and the dual inoculation treatment regulated multiple pathways，including 2-oxocarboxylic acid metabolism and glycolysis. Under salt stress，the levels of endogenous hormones in walnut seedling roots changed，with a decrease in JA，SA，and IAA content and an increase in ABA content. Pre-inoculation with mycorrhizal fungi increased the levels of JA，SA，and IAA in the roots of walnut seedlings under salt stress. Among these，P. indica showed a greater ability to enhance JA and IAA levels，while dual inoculation significantly reduced ABA content. In summary，single and dual inoculations with F. mosseae and P. indica can colonize and form symbionts in the roots of walnut seedlings，promoting hormone synthesis and hormone signaling pathways，thereby enhancing the salt tolerance of walnut seedlings. The synergistic effect was more pronounced in the dual inoculation treatment.

Key words: walnut, salt stress, mycorrhizal fungi, untargeted metabolomics, plant hormones