Regulation of Decomposition and Methane Dynamics across Natural, Commercially Mined, and Restored Northern Peatlands Nathan Basiliko, 1,5, * Christian Blodau, 1,2 Charlotte Roehm, 1,2,3 Per Bengtson, 4 and Tim R. Moore 1 1 Department of Geography and Centre for Climate and Global Change Research, McGill University, 805 Sherbrooke St. West QC H3A 2K6, Montreal, Canada; 2 Limnological Research Station and Department of Hydrology, University of Bayreuth, 95444 Bayreuth, Germany; 3 De ´ partement des Sciences Biologiques, Universite ´ du Que ´ bec a ` Montre ´ al, CP 8888 succursale Centre Ville QC H3C CP8, Montreal, Canada; 4 Department of Forest Sciences, University of British Columbia, 2424 Main Mall, BC V6T 1Z4, Vancouver, Canada; 5 Department of Geography, University of Toronto, Mississauga, 3359 Mississauga Rd. North, Mississauga L5L 1C6, ON, Canada ABSTRACT We examined aerobic and anaerobic microbial car- bon dioxide (CO 2 ) and methane (CH 4 ) exchange in peat samples representing different profiles at nat- ural, 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 CO 2 and CH 4 production, in agreement with previous studies. Owing mainly to wetter conditions, CH 4 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 CO 2 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 micro- bial CO 2 and CH 4 dynamics using stepwise regres- sion analysis among all sites and soil depths. Aerobic and anaerobic decomposition of peat was con- strained by organic matter quality, particularly phosphorus (P) and carbon (C) chemistry, and clo- sely linked to the size of the microbial biomass sup- ported 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 pro- portion of the total microbial biomass, there were no links between total microbial biomass and CH 4 production. Methane oxidation was controlled by the same factors influencing CH 4 production, lead- ing to the conclusion that CH 4 oxidation is primarily controlled by substrate (that is, CH 4 ) availability. Although restoring hydrology similar to natural sites may re-establish CH 4 dynamics, there is geographic or site-specific variability in the ability to restore peat decomposition dynamics. Key words: carbon dioxide; FTIR spectroscopy; lipids; methane oxidation; microbial biomass; nitrogen; nutrients; peat; phosphorus; roots. Received 25 February 2007; accepted 10 July 2007; published online 22 August 2007. *Corresponding author; e-mail: nathan.basiliko@utoronto.ca Ecosystems (2007) 10: 1148–1165 DOI: 10.1007/s10021-007-9083-2 1148