Effects of disturbance on seasonal CO 2 dynamics in two boreal forest sites underlain by permafrost

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 disturbed environments underlain by permafrost requires a comprehensive understanding of soil respiration dynamics. This study investigated the impact of surface disturbance on seasonal soil biological properties in a boreal forest ecosystem near Fairbanks, Alaska. Further, we sought to identify the key environmental and geochemical factors influencing soil biology in the undisturbed and disturbed soils. Our results revealed a substantial rise in soil respiration at the disturbed boreal forest site, which exhibited a 14.4 % overall increase in CO2 efflux compared to the undisturbed site. This effect was most pronounced during the summer, when the increase in CO2 efflux peaked at 20 %. This heightened respiratory activity was directly linked to significantly warmer soil conditions, with the mean annual soil temperature at the disturbed site measuring 0.60±0.16 °C, in stark contrast to the sub-zero temperatures of -0.37±0.08°C at the undisturbed site. Furthermore, the disturbed site had 30 % higher bacterial community richness, 1 % higher total mean C and 0.03 % higher total mean N concentration levels, and 11.9 % higher pH values in the subsoil layer, as well as a 147 % deeper maximum active thaw depth, suggesting potential controls underlying the variation in CO2 efflux. Our research underscores the essential importance of considering the rise in carbon emissions from anthropogenically disturbed soils underlain by permafrost, 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 disturbed permafrost environments, ultimately informing more accurate predictions of carbon fluxes in these ecosystems.