The effects of plant communities on methanogenesis and carbon dynamics in boreal peatlands
Abstract: Peatlands are a vital part of the global carbon cycle, storing vast amounts of carbon in organic material in the form of peat which is formed by slow decomposition of biomass due to cold, anoxic and low pH environment. Peatlands also emit methane (CH4), a potent greenhouse gas with 28 times stronger warming potential than carbon dioxide (CO2). The net C emissions of peatlands depend on wetland type and changes in environmental conditions, such as water table level or peat temperature, and the resulting balance between CH4 emissions and C uptake due to peat formation. The aim of this study was to research how plant communities and other controlling factors such as temperature, water table, LAI and wetland type affect both the atmospheric carbon flux and the belowground concentrations of CH4 and CO2. Additionally, stable carbon isotopes measurements were taken to gain further insight into the biogeochemistry of methanogenesis. The measurements were taken from Sphagnum dominated bog hummocks and Carex dominated fen lawns. Vegetation manipulations were conducted to the measurement plots to investigate the effects of plant communities on carbon dynamics, with three treatments: 1. removal of vascular plants and mosses, 2. Removal of vascular plants but mosses intact, 3. All vegetation intact. The study site is in Southern Finland at the Siikaneva peatland complex. Measurements were taken in 2018, between MaySeptember from an ombrotrophic bog and an oligotrophic fen. The measurement period was exceptionally dry with unusually low WT levels. Because of this, many of the previously observed correlations were not found. CH4 fluxes were mixed between bog and fen, depending on vegetation treatment. Mean belowground CH4 concentrations were generally slightly higher for the Fen site. Concentrations quickly grew with depth, at 50 cm depth, concentrations were multiple orders of magnitude higher than at the 7-20 cm depths with highest measurements being >500 000 ppm. δ13C-CH4 generally decreased with depth as the hydrogenotrophic methanogenesis pathway became more prevalent. Vegetation manipulations had mixed effects on CH4 flux and Leaf-area index didn’t show a strong linear correlation with CH4 flux. CH4 flux was also insensitive to water table, however aerenchymous plant mediated CH4 transport was likely not the cause, as the vegetation removal treated plots also showed similar insensitivity to WT. Removal of vascular plants and mosses generally reduced CH4 fluxes. Bog hummocks with moss intact but vascular plants removed had lowest CH4 fluxes. In conclusion, most environmental variables didn’t show strong correlations with CH4. No single variable clearly explained the differences in CH4 flux. Belowground concentrations strongly depend on depth and wetland type with fen having higher mean concentrations. Removal of vegetation generally reduced CH4 fluxes.
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