Desiccation-Hydration Cycles Regulate Transcriptional Responses in the Antarctic Moss Polytrichastrum alpinum and Its Microbiome

Frequent hydration–desiccation cycles in Antarctica impose strong selective pressures on bryophytes physiology and associated microbiota. Here, we investigated physiological and transcriptional responses of the Antarctic moss Polytrichastrum alpinum and its associated microbial communities under controlled hydration, desiccation and rehydration conditions. Desiccation induced strong but reversible physiological and molecular changes, with most gene expression patterns returning toward hydrated states upon rehydration, indicating efficient recovery of metabolic activity. This response involved coordinated regulation of stress-associated gene groups, including LEA proteins, heat-shock proteins and components of ABA and calcium signalling. Furthermore, field-collected samples exhibited transcriptional profiles similar to desiccated material, suggesting that this species naturally operates in a persistently water-limited state. Associated bacterial and fungal communities showed coordinated shifts in both composition and functional activity during the experiment, particularly in pathways related to carbon and amino acid metabolism. These results highlight the resilience of Antarctic P. alpinum and its microbiome under increasing environmental variability driven by climate change.