CO2 and CH4 Fluxes of the Epiphytic Lichen Bryoria simplicior in a Permafrost-Affected Siberia: From Field Observations to Laboratory Incubations

High-latitude climate change studies have mainly disregarded the role of epiphytic lichens in the greenhouse gas (GHG) budgets of Siberian permafrost ecosystems. In the permafrost-affected Middle Siberian region, the actual and potential fluxes of CO2 and CH4 from transplants of Bryoria simplicior inhabiting larch trees have been evaluated. Seasonal field measurements (June–August 2025) were combined with laboratory aerobic incubations under simulated polar-day conditions at 50%, 100%, and 200% thallus water contents. Field studies demonstrated mixed CO2 flux dynamics, with net CH4 consumption prevailing, although CH4 release occurred during prolonged rainfall. Incubations demonstrated potential CO2 and CH4 emissions. While Bryoria showed net CH4 uptake under dry field conditions, incubation experiments revealed its inherent capacity for both GHG release and uptake. Lichen water content and the combined light-temperature regime (photoperiod) had a significant impact on CO2 fluxes, whereas CH4 fluxes showed primarily a light-associated response. These findings highlight the susceptibility of lichen-mediated GHG exchange to moisture and light-temperature conditions, with potential implications for boreal C budgets in permafrost ecosystems under varying precipitation patterns.