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The large accumulation of carbon in peatlands arises from slow organic matter decomposition where microorganisms and their enzyme activities play a critical role. However, there is a dearth of studies on the natural patterns of peatland microbial enzyme activity and inhibitory phenolic compounds over seasons, and across a range of depths and biogeochemically different peatland types. We report the spatiotemporal patterns for phenol oxidases, phenolics, and a suite of five key hydrolase enzymes at two depths in two ombrotrophic bogs, mineral poor and rich fens, and a forested basin swamp over the growing season. Results obtained using linear fixed and mixed effect models suggest that phenol oxidase activity varies significantly with temperature and, to a lesser extent pH, leading to a breakdown of inhibitory phenolics and increased hydrolase enzyme activity across all peatland types. Overall, enzyme activity decreased significantly with depth and showed significant variation over the course of the growing season with a minimum in the spring and a maximum in the summer and fall. Enzyme activities were generally greatest in the rich fen and lowest in the forested basin swamp with no significant difference between bogs and poor fens. Site-specific factors such as nutrient availability explain deviations from these patterns. Our results illustrate the widespread but conditional applicability of the enzyme-latch mechanism to peatlands and the vulnerability of the peatland soil organic carbon stock to climate warming. [ABSTRACT FROM AUTHOR]

We investigated the response of CO2 and CH4 production to a water table fluctuation and a SO42− pulse in a bog mesocosm. Net gas production rates in the mesocosm were calculated from concentration data by diffusive mass-balances. Incubation experiments were used to quantify the effect of SO42− addition and the distribution of potential CO2 and CH4 production rates. Flooding of unsaturated peat resulted in rapid depletion of O2 and complex patterns of net CH4, CO2, and H2S production. Methane production began locally and without a time lag at rates of 3–4 nmol cm−3 d−1 deeper in the peat. Similar rates were determined after a time lag of 10–60 days in the surface layers, whereas rates at lower depths declined. Net CO2 production was largest immediately after the water table position was altered (100–300 nmol cm−3 d−1) and declined to −50–50 nmol cm−3 d−1 after a few weeks. SO42− addition (500 mM) significantly increased potential CH4 production rates in the surface layer from an average of 132–201 nmol cm−3 d−1 and reduced it below from an average of 418–256 nmol cm−3 d−1. Our results suggest that deeper in the peat (40–70 cm) under in situ conditions, methanogenic populations are less impaired by unsaturated conditions than in the surface layers, and that at these depths after flooding the substrate availability for CH4 and DIC production is significantly enhanced. They also suggest that methanogenic and SO42−-reducing activity were non-competitive in the surface layer, which might explain contradictory findings from field studies. [Copyright &y& Elsevier]