Effect of changing tundra vegetation on greenhouse gas emissions from Arctic permafrost soil

The Arctic is warming rapidly, causing permafrost thaw and vegetation shifts. As a result, shrubs and trees from lower latitudes are encroaching into the tundra, altering biomass distribution above and below ground. These changes impact greenhouse gas (GHG) emissions by influencing litter input, root distribution, and microbial activity. A key mechanism in GHG production in soils is the rhizosphere priming effect, where labile carbon inputs from plants into the soil stimulate microorganisms to produce enzymes that decompose both labile and recalcitrant soil organic matter (SOM). However, the effects of rhizosphere priming on SOM decomposition and its influence on greenhouse gas emissions under natural conditions remain poorly understood. To address this, we simulated sub-Arctic vegetation changes in a controlled environment using tundra soil and plants sampled from the Northwest Territories, Canada. The soil was processed, homogenized, and placed into macrocosm chambers while preserving the original horizon sequence. The experiment included four vegetation types and one control, with plant species that are characteristic for the transition from sub-Arctic to lower Arctic bioclimate zones and included a small tree (Picea mariana), deciduous shrubs (Betula glandulosa, Alnus viridis) and graminoids (Eriophorum vaginatum, Carex sp.). Over three months, representing one growing season, weekly soil pore gas samples were taken at different depths, and surface efflux was measured additionally every three weeks. Preliminary results indicate that soil pore gas concentrations of CO₂ increased with depth and over the experiment's duration across all vegetation groups and the control, and showed variability among vegetation types. Soil pore gas concentrations will be compared with soil efflux, dissolved organic carbon, microbial carbon contents, extracellular enzyme activity, and other parameters currently under evaluation. These data will help us to elucidate the role of woody plant species for permafrost soil processes and their contribution to GHG production in Arctic tundra ecosystems.