Objective The aims were to elucidate the response characteristics of wheat rhizosphere fungal community structure and function to salt stress in coastal saline-alkali soils, in order to provide a basis for deciphering the regulatory mechanisms of soil fungi under salt stress and mining salt-tolerant microbial resources.

Method Based on soil soluble salt content, three salt stress treatments were established: low salinity stress level (LS, < 2 g kg⁻¹), medium salinity stress level (MS, 2 - 4 g kg⁻¹), and high salinity stress level (HS, > 4 g kg⁻¹). Wheat plants and rhizosphere soil samples were collected. Soil pH, electrical conductivity (EC), soluble salt content, water content, and nutrient indices were determined. Wheat biomass, Na ⁺ /K ⁺ ion content, and hormone levels were analyzed. The structure and function of fungal communities were analyzed based on ITS gene high-throughput sequencing technology. Key responsive taxa were screened using the random forest model, and fungal functions were predicted using FUNGuild.

Result With increasing salt stress intensity, soil EC and total soluble salts increased significantly (P < 0.05). Above-ground biomass of wheat significantly decreased under high salinity stress with significant Na ⁺ accumulation and K ⁺ reduction in plants (P < 0.05), indicating that high salinity stress severely disrupted ion homeostasis and inhibited growth. Salinity stress significantly affected fungal community structure. Ascomycota was the dominant phylum, with Blumeria, Mortierella, and Pseudogymnoascus as dominant genera. The relative abundances of Pseudogymnoascus and Curvularia changed significantly with increasing salinity stress levels (P < 0.05). Random forest analysis identified 15 key OTUs, some OTUs belonged to Chaetomium and Pseudogymnoascus, with good indicators of salinity stress levels. Fungal community nutritional strategies changed significantly with increasing salinity stress levels. The proportion of the Pathotroph-Saprotroph-Symbiotroph guild significantly increased from 7.34% under low salinity stress to 24.45% under high salinity stress, becoming one of the dominant nutritional guilds under high salinity stress.

Conclusion Under high salinity stress, wheat likely enhances its adaptability to salinity stress by recruiting dominant salt-tolerant fungi such as Pseudogymnoascus and Chaetomium in the rhizosphere. The shift in the community from predominantly single or dual nutritional guilds towards a more flexible mixed strategy involving multiple guilds may be an important mechanism for fungi to maintain ecological functional stability and adaptability in saline-stressed environments.