Interactive effects of vegetation and water table depth on belowground C and N mobilization and greenhouse gas emissions in a restored peatland

Aims: This study assesses the relative effects of hydrology and colonization by vascular plants on belowground C and N mobilization, and emission of CO2 and CH4 in an extracted bog under restoration in Alberta (Canada). Methods: A wet (high water table) and dry (low water table) area were identified at the site and plots with cottongrass (Eriophorum vaginatum) or bare peat were established in each area. Plant growth, peat and porewater dissolved C (DOC) and N (TDN), microbial biomass and the emissions of CO2 and CH4 were monitored at the plots throughout the growing season. Results: The largest concentrations of DOC were measured in dry and bare sites. Lower E2:E3 ratios suggested a higher aromaticity of the DOC at these sites that were net sources of CO2 and CH4. The concentration of TDN was greater in plots with cottongrass and high water table, supporting a more abundant microbial biomass. Cottongrass dominated plots also had larger gas emissions as compared to bare plots even though they were net C sinks due to their high photosynthetic rates. Conclusion: Maintaining a high water table is key to reducing peatland C losses. While vascular plant presence seems to prime the release of N and greenhouse gases, the inputs of C exceeded the losses and recovered the C sink function of the peatland ecosystem in the short term. Carbon inputs are maximized under high water table and plant presence.