Thermal filtering reveals a cryptic reservoir of thermotolerant yeasts in Sub-Antarctic soils

Global climate change is accelerating ecological transformation in Sub-Antarctic ecosystems, where resident biota exhibit narrow thermal tolerances. While microbial responses to warming are increasingly documented, the role of soil yeasts, key players in organic matter decomposition, remains poorly understood. Here, we show that warming acts as a deterministic filter, triggering a profound community restructuring that favors a cryptic reservoir of thermotolerant taxa. Using species-sorting and thermal profiling, we found that elevated temperatures (up to 35°C) significantly reduced alpha diversity and richness. This filtering shifted communities from cold-adapted assemblages to simpler, thermotolerant lineages. Thermal sorting revealed hidden culturable diversity, notably an increase in Candida spp., with Candida railenensis and Candida parapsilosis found only under warm conditions. Physiological profiling showed C. railenensis had broad thermal plasticity, while C. parapsilosis was high-temperature specialized. Additionally, warming nearly eliminated ectomycorrhizal guilds and increased saprotrophs, suggesting shifts in carbon processing and organic matter decomposition. Furthermore, our results indicate that sustained warming reduces functional redundancy and broadens reservoirs for opportunistic pathogens such as C. parapsilosis, which thrive near human body temperatures. These findings highlight the importance of including yeasts in climate models to predict future biogeochemical changes and biological risks in warming cold ecosystems.