biostudies-literatureStansfield ARDivision of Environmental BiologyLehigh University30https://www.ebi.ac.uk/biostudies/studies/S-EPMC12808267biostudies-literatureUnknown89(1)High-latitude ecosystems are undergoing rapid ecological changes in response to climate warming. While some changes are well studied, the responses of microbial communities remain less understood. Testate amoebae, shell-producing protists well preserved in peat, provide a means to reconstruct past microbial dynamics. Mixotrophic taxa such as Archerella flavum host algal endosymbionts (zoochlorellae), allowing both heterotrophic and phototrophic energy acquisition. Previous work has demonstrated that these pathways result in different δ¹³C values. We applied a novel stable isotope approach to a peat core from the North Slope of Alaska to reconstruct changes in phototrophy by Archerella flavum. δ¹³C values were measured on Archerella flavum tests (i.e. shells) and SphagMicrobial ecologyRecent Changes in the Use of Phototrophy by a Mixotrophic Testate Amoeba Inferred from δ<sup>13</sup>C Measurements from an Arctic Peat Core.PMC12808267DEB-1802810College of Arts & Sciences Dean's Research FellowshipStansfield ARNelson DMJohnson JBooth RKfalseRecent Changes in the Use of Phototrophy by a Mixotrophic Testate Amoeba Inferred from δ<sup>13</sup>C Measurements from an Arctic Peat Core.High-latitude ecosystems are undergoing rapid ecological changes in response to climate warming. While some changes are well studied, the responses of microbial communities remain less understood. Testate amoebae, shell-producing protists well preserved in peat, provide a means to reconstruct past microbial dynamics. Mixotrophic taxa such as Archerella flavum host algal endosymbionts (zoochlorellae), allowing both heterotrophic and phototrophic energy acquisition. Previous work has demonstrated that these pathways result in different δ¹³C values. We applied a novel stable isotope approach to a peat core from the North Slope of Alaska to reconstruct changes in phototrophy by Archerella flavum. δ¹³C values were measured on Archerella flavum tests (i.e. shells) and Sphag2025-01-01T00:00:00Z2025 Dec2026-05-31T03:17:13.71Z2026-05-31T03:10:19.668ZS-EPMC128082674142009910.1007/s00248-025-02681-3