A Bog By Any Other Name: Do All ‘Bogs' Have Similar Anaerobic Carbon Dynamics?.

Low pH, Sphagnum-dominated peatlands are, at first glance, generally considered ‘bogs’; however, there is growing evidence that anaerobic carbon biogeochemistry can differ dramatically between these similarly categorized peatlands.  We compared seasonal CH₄ fluxes, anaerobic C cycling, and microbial communities in three Sphagnum-dominated peatlands in northern Minnesota.  The S1 peatland is home to the new SPRUCE climate change experiment and is a weakly minerotrophic (i.e., with groundwater connectivity) system with well-developed hummocks and hollows.  Bog Lake Fen (BLF) is a poor fen with less developed microtopgraphy and is dominated by a moss and graminoid lawn.  Zim is a truly ombrotrophic (i.e., rain fed) bog characterized by extensive Sphagnum hummocks.

Net CH₄ emissions were highest in BLF and S1 but very low in Zim where isotopic evidence demonstrates that methane oxidation was important.  Porewater CH₄ concentrations were similar at all sites, but isotopic data suggest that acetoclastic methanogenesis was important in the surface of BLF while hydrogenotrophic methanogenesis dominated throughout the soil profiles at S1 and Zim.  Rates of CH₄ production measured in July of 2013 decreased with depth in S1 hollows and BLF but were very low at all depths in S1 hummocks and Zim soils.    Potential CH₄ production measured over 6 months in laboratory incubations showed that surface soils from Zim produced comparable CH₄ to other sites.  Chemical characterization of DOM and solid peat generally indicated that S1 and Zim were similar at a particular depth and could not explain differences in CH₄ production potentials. 

There were no differences in mcrA gene or transcript abundance among sites, but the mcrA transcript-to-gene ratio was highest in S1, in concordance with its high CH₄ production potential.  Surface peat pmoA gene and transcript abundances were much higher in Zim and BLF compared to S1, and the transcript-to-gene ratio was highest in Zim, supporting an interpretation of high CH₄ oxidation at that site.

Our results indicate substantial differences in anaerobic carbon cycling in these three peatlands despite them all having low pH and being covered by Sphagnum mosses.