Methanogenesis and Methanogen Diversity in Three Peatland Types of the Discontinuous Permafrost Zone, Boreal Western Continental Canada

Because recent patterns of permafrost collapse in boreal peatlands appear to enhance emissions of CH ₄ to the atmosphere, we examined methanogenesis and methanogen diversity in peat soil from peatlands with and without permafrost in two peatland complexes situated in continental western Canada. Peat soil from the active layer of permafrost bogs had very low rates of CH ₄ production (ca. 10 nmol g ⁻¹ day ⁻¹ ), and we were unable to PCR-amplify 16s rRNA gene sequences using Archaea-specific primers in four peat samples. Surface peat soil from continental bogs with no permafrost supported moderate rates of CH ₄ production (20–600 nmol g ⁻¹ day ⁻¹ ), with maximum rates in soil located close to the mean water table level. Additions of ethanol stimulated CH ₄ production rates, suggesting metabolic substrate limitations. Peat from internal lawns, which have experienced surface permafrost degradation in the past 150 years, had very rapid rates of CH₄ production (up to 800 nmol g ⁻¹ day ⁻¹ ) occurring within the soil profile. Concomitant rates of anaerobic CO ₂ production were greater in continental bogs (ca. 6 μmol g ⁻¹ day ⁻¹ ) than in internal lawns (ca. 4 μ mol g ⁻¹ day ⁻¹ ) or in permafrost bogs (2.8 μ mol g ⁻¹ day ⁻¹ ). Analysis of the 16s rRNA gene for Archaea in the continental bog indicated mostly sequences associate with Methanobacteriales and RC-I with a Methanosarcinaceae sequence in the deepest peat soil. In the internal lawn, Methanosarcinaceae were most common in peat soil with a Methanosaetaceae sequence in the deepest peat soil. This study showed that patterns of discontinuous permafrost and ongoing permafrost degradation in boreal regions create patchy soil environments for methanogens and rates of methanogenesis.

Keywords:

• anaerobic carbon mineralization
• boreal wetland
• Canada
• CO₂
• CH₄
• ecosystems
• peat soils
• discontinuous permafrost
• Ribosomal-RNA sequences
• trace metal

Acknowledgments

Research support provided by a grant from the USA National Science Foundation (BSR-9727800). The publication does not necessarily reflect the views of NSF, which did not review the material before publication. We thank Mark Dettling for ICP analyses and three Cornell undergraduate students, Charly Ann Newman, Michael Seidman-Zager, and Aaron Stupple for assistance with the molecular analyses. Two reviewers made helpful suggestions that improved the clarity of the presentation, for which we are grateful.