Soil disturbances affect greenhouse gas dynamics, soil carbon stability and microbial community in drained peatland forest

Soils in drained peatland forests are a large source of greenhouse gas (GHG) emissions, and stand regeneration or soil disturbances may accelerate the loss of remaining carbon stocks. Disturbances such as windthrow, harvesting and soil preparation alter canopy cover, increase residue inputs, modify soil microtopography and microclimate, potentially shifting soil processes. We conducted a field experiment in a drained peatland forest in southern Finland and simulated two disturbance types – residue cover and topsoil removal – in both canopy-covered forest and clearcut sites to assess their short-term effects on GHG emissions, soil organic carbon (SOC) stability and microbial communities. Residue addition increased CO 2 and N 2 O emissions in the canopy-covered forest during the two-year post-treatment period. Topsoil removal reduced CO 2 emissions but increased N 2 O emissions, weakened the CH 4 sink and converted the clearcut into a net CH 4 source. In the canopy-covered forest dominated by ectomycorrhizal (EcM) fungi, residue addition reduced fungal biomass while enhanced SOC stability. In contrast, topsoil removal eliminated ground vegetation and roots, reduced plant-derived tannins and root-associated EcM fungi, and decreased SOC stability. Disturbance effects on microbial communities and SOC pools were minor in the clearcut, likely because microbial community composition and soil processes had already shifted following canopy removal. Our results demonstrate that soil disturbances disrupted soil processes, elevated short-term GHG emissions and increased spatial heterogeneity in soil microbial communities and SOC pools. The stronger responses observed in the canopy-covered forest than in the clearcut highlight the importance of stand condition when evaluating the disturbance impacts in peatland forests.