Regulation of decomposition and methane dynamics across natural, commercially mined, and restored northern peatlands

We examined aerobic and anaerobic microbial carbon dioxide (CO2) and methane (CH4) exchange in peat samples representing different profiles at natural, mined, mined-abandoned, and restored northern peatlands and characterized the nutrient and substrate chemistry and microbial biomass of these soils. Mining and abandonment led to reduced nutrient and substrate availability and occasionally drier conditions in surface peat resulting in a drastic reduction in CO2 and CH4 production, in agreement with previous studies. Owing mainly to wetter conditions, CH4 production and oxidation were faster in restored block-cut than natural sites, whereas in one restored site, increased substrate and nutrient availability led to much more rapid rates of CO2 production. Our work in restored block-cut sites compliments that in vacuum-harvested peatlands undergoing more recent active restoration attempts. The sites we examined covered a large range of soil C substrate quality, nutrient availability, microbial biomass, and microbial activities, allowing us to draw general conclusions about controls on microbial CO2 and CH4 dynamics using stepwise regression analysis among all sites and soil depths. Aerobic and anaerobic decomposition of peat was constrained by organic matter quality, particularly phosphorus (P) and carbon (C) chemistry, and closely linked to the size of the microbial biomass supported by these limiting resources. Methane production was more dominantly controlled by field moisture content (a proxy for anaerobism), even after 20 days of anaerobic laboratory incubation, and to a lesser extent by C substrate availability. As methanogens likely represented only a small proportion of the total microbial biomass, there were no links between total microbial biomass and CH4 production. Methane oxidation was controlled by the same factors influencing CH4 production, leading to the conclusion that CH4 oxidation is primarily controlled by substrate (that is, CH4) availability. Although restoring hydrology similar to natural sites may re-establish CH4 dynamics, there is geographic or site-specific variability in the ability to restore peat decomposition dynamics.