Effects of permafrost thaw on seasonal soil CO₂ efflux dynamics in a boreal forest site

Abstract. Permafrost regions in subarctic and arctic areas harbor substantial carbon reserves, which are becoming increasingly vulnerable to microbial decomposition as soils warm. As the seasonally thawed active layer deepens and anthropogenic disturbances escalate, accurately predicting carbon fluxes from thawed permafrost requires a comprehensive understanding of soil respiration dynamics. This study aimed to investigate the impact of disturbance on soil respiration rates and identify the key environmental and geochemical factors influencing these processes in a boreal forest ecosystem near Fairbanks, Alaska. The disturbed site demonstrated an increase in mean annual soil temperatures, recorded at 0.60 ± 0.16 °C, along with a 14.4 % rise in mean annual microbial activity, which peaked at 20 % during the summer, in contrast to the undisturbed site, which had a mean annual temperature of -0.37 ± 0.08 °C. Furthermore, bacterial and fungal community composition differed significantly between the two sites, suggesting a potential mechanism underlying the variation in CO₂ efflux. Our research underscores the essential importance of considering the rise in carbon emissions from anthropogenically disturbed soils in permafrost areas, which are frequently neglected in assessments of the carbon cycle. This study contributes to a deeper understanding of the complex interactions governing soil respiration in thawing permafrost, ultimately informing more accurate predictions of carbon fluxes in these ecosystems.