Symbiotic microbiota of cryptogams regulate VOC emissions and nitrogen fixation in subarctic tundra

Cryptogams (mosses, lichens and liverworts) are widespread and can influence nitrogen cycling and biosphere–atmosphere exchange of volatile organic compounds (VOCs), especially in high-latitude ecosystems. However, the contributions of their symbiotic microbiota (e.g. cyanobacteria and other diazotrophs) to both N fixation and VOC emissions remain relatively underexplored. Here, we conducted controlled incubations of multiple subarctic cryptogam species before and after the removal of their symbiotic microbiota on the surface. We quantified N fixation activity using acetylene reduction assays and characterised VOC emissions using complementary GC–MS and PTR–TOF–MS measurements. Preliminary results showed that N fixation rates decreased significantly in several moss species after the removal of the symbiotic microbiota, whereas responses in lichens and liverwort were weaker or non-significant. Both total VOC emission rates and composition were altered for most species. A random forest model identified several sesquiterpenes (SQTs) as key discriminant compounds; their emission rates were increased after the removal of surface-associated symbionts from the cryptogams. Partial least squares analysis further revealed coupling between selected VOC fingerprints and N fixation rates. Overall, these results demonstrate that removable surface symbionts can concurrently regulate cryptogam N fixation and VOC emissions in subarctic systems, with potential implications for ecosystem N inputs and VOC-mediated atmospheric chemistry.