Plant functional group effects on peat carbon cycling in a boreal rich fen

Dominant plant functional groups (PFGs) found in boreal rich fens include sedges, grasses, horsetails, and cinquefoils (obligate wetland shrubs). Precipitation regime shift and permafrost thaw due to climate change will likely trigger changes in fen plant community structure through shifts in these PFGs, and it is thus crucial to understand how these PFGs will impact carbon cycling and greenhouse gas dynamics to predict and model peatland-climate feedbacks. In this study, we detail the above and belowground effects of these PFGs on aspects of carbon cycling using a mesocosm approach. We hypothesized that PFGs capable of aerating the rhizosphere (sedges, horsetails, and grasses) would oxidize the belowground environment supporting higher redox potentials, a favorable environment for decomposition, and higher CO2:CH4 in pore water and gas efflux measurements than PFGs lacking aerenchyma (cinquefoil, unplanted control). Overall, sedges, horsetail and grasses had an oxidizing effect on rhizosphere pore water chemistry, producing an environment more favorable for methanotrophy during the growing season, as supported by an approximate isotopic enrichment of pore water methane (delta(CH4)-C-13) by 5 parts per thousand, and isotopic depletion in pore water carbon dioxide (delta(CO2)-C-13) by 10 parts per thousand, relative to cinquefoil treatments. Cinquefoil and unplanted control treatments fostered a reducing environment more favorable for methanogenesis. In addition, cinquefoil appeared to slow decomposition in comparison with the other PFGs. These findings, paired with PFG effects on oxidation-reduction potential and CO2 and CH4 production, point to the ability of rich fen plant communities to moderate biogeochemistry, specifically carbon cycling, in response to changing climatic conditions.