Special Fungal Community Structure Formed by Typical Halophytes in the Rhizosphere Soil Under the Synergistic Action of Different Saline and Alkaline Environments

To adapt to a habitat, halophytes growing at the same saline–alkali levels develop their unique rhizosphere microbial communities, whereas same plant species growing at different saline–alkali levels have different rhizosphere microbial communities. Therefore, understanding the rhizosphere microbial community structure of halophytes in different saline–alkali soils can help explore the microbial diversity and functional potential of important soil microorganisms. In this study, rhizosphere soils of three typical halophytes, namely, Halocnemum strobilaceum, Phragmites communis, and Halostachys caspica, growing at severe, heavy, and moderate saline–alkali soils, respectively, were collected from southern Xinjiang. The community structure and physicochemical properties of fungal species in the total nine rhizosphere soils were investigated. Furthermore, the differences in the fungal community structure, diversity, and ecological functions were analyzed in terms of the extent of saline–alkali level and host plant specificity. Rhizosphere soils in the nine habitats had different physicochemical properties. In terms of host plant type, rhizosphere fungal species diversity and richness were the highest in P. communis, followed by H. caspica and H. strobilaceum. The fungal community diversity and richness followed the pattern of moderate > severe > heavy in different soil salinity and alkali types. Although the three host plants had similar rhizosphere fungal community structures under moderate and heavy saline–alkali conditions, these varied significantly under extremely severe saline–alkali conditions. In total, 315 species were identified across all samples, and they were affiliated with 12 phyla, 37 classes, 69 orders, 138 families, and 244 genera. The number of jointly owned ASVs was 189. In the nine habitats, Ascomycota and Basidiomycota were the dominant phyla, while Alternaria, Neocamarosporium, Filobasidium, and Acremonium were the common dominant genera. A prediction of fungal community functions revealed pathotroph-saprotroph-symbiotroph and saprotrophs to be dominant. At the same saline–alkali level, the functional clustering distance of fungal communities was closer. Factors such as soil organic matter (SOM), available nitrogen (AN), electronic conductivity (EC), and pH contributed to the distribution of microbial communities. This study revealed both similarities and distinctions in the composition of fungal communities within the rhizosphere soils of the three typical halophytes thriving in various saline–alkali habitats. At moderate and heavy saline–alkali levels, the fungal community structures were markedly influenced by the severity of salinity and alkalinity. In extremely severe saline–alkali soils, the host plant type significantly affected the fungal community structure. Ultimately, these findings lay a theoretical foundation for the improvement of soil and crop yield in saline–alkali land.