Diversity and Community Structure of Rhizosphere Arbuscular Mycorrhizal Fungi in Songnen Grassland Saline–Alkali-Tolerant Plants: Roles of Environmental Salinity and Plant Species Identity

The Songnen Grassland, a typical saline–alkali ecosystem in Northeast China, is increasingly degraded by soil salinization. Arbuscular mycorrhizal fungi (AMF) are critical for enhancing plant tolerance to saline–alkali stress via root symbiosis. To investigate the species diversity and community structure of AMF in the rhizosphere of salt-tolerant plants in the Songnen Grassland, this study combined morphological identification with high-throughput sequencing (based on virtual taxa, VTs, from the MaarjAM database) to analyze the composition and distribution characteristics of AMF in the rhizosphere of eight salt-tolerant plant species, including Arundinella anomala, Leymus chinensis, Taraxacum mongolicum and others. Morphological identification revealed a total of 22 AMF species belonging to 7 genera. Among these, the genus Glomus was the dominant genus, comprising eight species (accounting for 36.4% of the total species), followed by the genus Acaulospora (five species, 22.7%), the genus Rhizophagus (four species, 18.2%), the genus Ambispora (two species, 9.1%), and the remaining genera each represented by one species (4.5%). High-throughput sequencing analysis identified a total of 40 virtual taxa (VTs) with clear taxonomic assignments belonging to six genera. The genus Glomus accounted for the highest proportion (34 VTs, 85%) with a relative abundance of 89.33%, representing the overwhelmingly dominant group. Rhizosphere soil electrical conductivity (EC) of the eight plant species indicated a significant gradient (high EC group: A–D and G, 2.07–2.61 mS/cm; low EC group: E, F, H, 0.20–0.48 mS/cm). The AMF diversity in the high EC group was significantly higher than that in the low EC group, indicating that AMF in the rhizosphere of salt-tolerant plants enhanced plant tolerance to high-salt environments, and their diversity did not decrease with increasing salinity but instead remained at a high level. Plant-specific AMF community characteristics were evident. Hierarchical clustering analysis further confirmed that the AMF community composition in the rhizosphere of Taraxacum mongolicum and Vicia amoena differed significantly from that of the other plant species, indicating that plant species have a key driving role in AMF community structure. These findings provide critical insights into the plant–AMF symbiotic mechanisms underlying saline–alkali adaptation and offer a theoretical basis for selecting efficient AMF strains to support ecological restoration of saline–alkali lands.