Distinct factors drive the diversity and composition of soil protists across vegetation types in the Qinghai-Tibet Plateau

• Protist communities exhibit significant variation across vegetation types. • Bacterial and fungal communities drive consumers and phototrophic protists. • Parasitic protist communities are associated with precipitation and soil C/N ratio. • Key bacterial and fungal taxa are predictors of core functional protist groups. Protists represent a pivotal component of the soil micro-food web, exerting critical roles in sustaining ecosystem functions. However, the distribution patterns and underlying mechanisms of distinct functional groups (consumers, parasites, and phototrophs) within high-altitude environments remain poorly understood. In this study, 18S rRNA gene amplicon sequencing was performed on 458 samples collected from five typical vegetations (alpine desert grassland, alpine grasslands, alpine meadow, alpine shrubland, and forest) across the Qinghai-Tibet Plateau. The results demonstrated that consumers dominated protist assemblages (77.6% relative abundance), primarily comprising taxa from Filosa-Sarcomonadea, Variosea and Tubulinea. Parasitic protists accounted for 11.1% of the community and were primarily represented by Apicomplexa and Oomycota. Phototrophic protists constituted 6.1% of the assemblage, with Chrysophyceae and Chlorophyceae being the dominant lineages. Protist alpha diversity was lowest in alpine desert steppe and highest in meadow and shrubland. In contrast, alpha and beta diversities of protist functional groups were predicted by distinct sets of environmental factors. Consumer and phototroph alpha diversity were best predicted by bacterial and fungal diversity; parasite alpha diversity was driven by soil chemistry. Beta diversity followed the same split: consumers and phototrophs responded to both biotic (e.g., microbial composition) and abiotic (e.g., pH, precipitation) factors; parasites responded only to abiotic factors (precipitation, moisture, C:N ratio). Furthermore, the core protist community was significantly influenced by bacterial and fungal communities. This study elucidates the differential assembly processes of protist functional groups under multi-stress environments, providing novel insights into microbial functional adaptation and ecosystem responses to environmental changes in high-altitude ecosystems.