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Contributed Poster

Session: Communities

PS 2-20 - Increased phototrophy in testate amoebae associated with recent warming on Alaska’s North Slope

Monday, August 7, 2023
5:00 PM – 6:30 PM PDT
Location: ESA Exhibit Hall

    Presenting Author(s)

  • AS

    Alexis Stansfield

    Lehigh Univesity
    Bethlehem, PA, United States

    • Coauthor(s)

  • RB

    Robert K. Booth

    Lehigh Univesity
    Bethlehem, Pennsylvania, United States

  • DN

    David M. Nelson

    Professor
    University of Maryland Center for Environmental Science, Maryland, United States

  • JJ

    Jonathan Johnson

    University of Maryland Center for Environmental Science, United States

Abstract: Recent warming has resulted in ecological changes in the arctic, including shrub expansion and northward movement of boreal forest. However, much less is known about how microorganisms are responding to climatic and environmental changes within this carbon-rich region. Testate amoebae, a group of protists that produce decay-resistant shells (i.e., tests), are well-suited to paleoecological studies aimed at understanding microbial responses to arctic climate change. In peatland environments, testate amoebae are a key component of microbial food webs, feeding on bacteria, microalgae, and smaller protists. A few species of testate amoebae are mixotrophic, acquiring energy via photosynthesis using algal symbionts (zoochlorellae) in addition to heterotrophic food sources. Although most studies of carbon cycling in peatlands have not taken microorganisms into account, recent work indicates that carbon intake by mixotrophic testate amoebae may be significant at the ecosystem level. Previous studies suggest that δ13C of mixotrophic amoeba tests reflects the relative contribution of zoochlorellae and heterotrophic food sources, because these two carbon sources have very distinct δ13C values. In this study, we made new measurements of δ13C of testate amoebae in living Sphagnum to confirm this previous work, and then measured changes in the δ13C of Sphagnum and Archerella flavum, a mixotrophic species, along a 14C-dated peat core collected from the North Slope of Alaska. Our primary objective was to assess the hypothesis that a longer snow-free season over the last several decades led to greater relative use of algal symbionts by this mixotrophic species. Our δ13C measurements provide a sub-decadally resolved record of changes in the relative use of carbon sources by Archerella flavum, and reveal that populations rapidly shifted toward greater relative use of algal symbionts in the late 1960s and 1970s, when the region experienced the onset of pronounced warming. Furthermore, fluctuations in the length of the snow-free season, measured in the vicinity of Toolik Lake since 2007, correspond with our δ13C measurements. Collectively the patterns are consistent with the hypothesis of increased algal symbiont use by Archerella flavum as the snow-free season has lengthened. Understanding how these changes may impact broader microbial communities and carbon cycling processes in high-latitude Sphagnum peatlands is not yet understood.