A novel framework for quantifying past methane recycling by Sphagnum‐methanotroph symbiosis using carbon and hydrogen isotope ratios of leaf wax biomarkers. (27th May 2014)

• Record Type: Journal Article
• Authors: Nichols, Jonathan E.; Isles, Peter D. F.; Peteet, Dorothy M.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 15:Number 5(2014:May)
• Page Start: 1827
• Page End: 1836
• Publication Date: 2014-05-27
• Subjects: Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1002/2014GC005242
• Languages: English
• ISSNs: 1525-2027

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>The concentration of atmospheric methane is strongly linked to variations in Earth's climate. Currently, we can directly reconstruct the total atmospheric concentration of methane, but not individual terms of the methane cycle. Northern wetlands, dominated by <italic>Sphagnum</italic>, are an important contributor of atmospheric methane, and we seek to understand the methane cycle in these systems. We present a novel method for quantifying the proportion of carbon <italic>Sphagnum</italic> assimilates from its methanotrophic symbionts using stable isotope ratios of leaf‐wax biomarkers. Carbon isotope ratios of <italic>Sphagnum</italic> compounds are determined by two competing influences, water content and the isotope ratio of source carbon. We disentangled these effects using a combined hydrogen and carbon isotope approach. We constrained <italic>Sphagnum</italic> water content using the contrast between the hydrogen isotope ratios of <italic>Sphagnum</italic> and vascular plant biomarkers. We then used <italic>Sphagnum</italic> water content to calculate the carbon isotope ratio of <italic>Sphagnum</italic>'s carbon pool. Using a mass balance equation, we calculated the proportion of recycled methane contributed to the <italic>Sphagnum</italic> carbon pool, "PRM." We quantified PRM in peat monoliths from three microhabitats in the Mer Bleue peatland complex. Modern studies have shown that water table depth and vegetation have strong influences on the peatland methane cycle on instrumental time scales. With this new approach, δ<sup>13</sup>C of <italic>Sphagnum</italic> compounds are now a useful tool for investigating the relationships among hydrology, vegetation, and methanotrophy in <italic>Sphagnum</italic> peatlands over the time scales of entire peatland sediment records, vital to our understanding of the global carbon cycle through the Late Glacial and Holocene.</p> </abstract>