title: An unexpected role for mixotrophs in the response of peatland carbon cycling to climate warming.
abstract: Mixotrophic protists are increasingly recognized for their significant contribution to carbon (C) cycling. As phototrophs they contribute to photosynthetic C fixation, whilst as predators of decomposers, they indirectly influence organic matter decomposition. Despite these direct and indirect effects on the C cycle, little is known about the responses of peatland mixotrophs to climate change and the potential consequences for the peatland C cycle. With a combination of field and microcosm experiments, we show that mixotrophs in the Sphagnum bryosphere play an important role in modulating peatland C cycle responses to experimental warming. We found that five years of consecutive summer warming with peaks of +2 to +8°C led to a 50% reduction in the biomass of the dominant mixotrophs, the mixotrophic testate amoebae (MTA). The biomass of other microbial groups (including decomposers) did not change, suggesting MTA to be particularly sensitive to temperature. In a microcosm experiment under controlled conditions, we then manipulated the abundance of MTA, and showed that the reported 50% reduction of MTA biomass in the field was linked to a significant reduction of net C uptake (-13%) of the entire Sphagnum bryosphere. Our findings suggest that reduced abundance of MTA with climate warming could lead to reduced peatland C fixation.
authors.affiliation: School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne EPFL, Ecological Systems Laboratory (ECOS), Station 2, 1015 Lausanne, Switzerland.|Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Site Lausanne, Station 2, 1015 Lausanne, Switzerland.
authors.forename: Vincent E J
authors.initials: VE
authors.lastname: Jassey
authors.affiliation: School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne EPFL, Ecological Systems Laboratory (ECOS), Station 2, 1015 Lausanne, Switzerland.|Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Site Lausanne, Station 2, 1015 Lausanne, Switzerland.
authors.forename: Constant
authors.initials: C
authors.lastname: Signarbieux
authors.affiliation: Centre d'Ecologie Fonctionelle et Evolutive (CEFE), CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, 1919 route de Mende, 34293 Montpellier, France.
authors.forename: Stephan
authors.initials: S
authors.lastname: Hättenschwiler
authors.affiliation: School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne EPFL, Ecological Systems Laboratory (ECOS), Station 2, 1015 Lausanne, Switzerland.|Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Site Lausanne, Station 2, 1015 Lausanne, Switzerland.|University of Ferrara, Department of Life Science and Biotechnologies, Corso Ercole I d'Este 32, I-44121 Ferrara, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Bragazza
authors.affiliation: School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne EPFL, Ecological Systems Laboratory (ECOS), Station 2, 1015 Lausanne, Switzerland.|Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Site Lausanne, Station 2, 1015 Lausanne, Switzerland.|Université de Franche-Comté - Laboratoire Chrono-Environnement, UMR CNRS/UFC 6249, F-25211 Montbéliard cedex, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Buttler
authors.affiliation: Université d'Orléans, ISTO, UMR 7327, 45071 Orléans, France.|BRGM, ISTO, UMR 7327, BP 36009, 45060 Orléans, France.|CNRS/INSU, ISTO, UMR 7327, 45071 Orléans, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Delarue
authors.affiliation: University of Neuchâtel, Laboratory of Soil Biology, Rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland.
authors.forename: Bertrand
authors.initials: B
authors.lastname: Fournier
authors.affiliation: Université de Franche-Comté - Laboratoire Chrono-Environnement, UMR CNRS/UFC 6249, F-25211 Montbéliard cedex, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Gilbert
authors.affiliation: Université d'Orléans, ISTO, UMR 7327, 45071 Orléans, France.|BRGM, ISTO, UMR 7327, BP 36009, 45060 Orléans, France.|CNRS/INSU, ISTO, UMR 7327, 45071 Orléans, France.
authors.forename: Fatima
authors.initials: F
authors.lastname: Laggoun-Défarge
authors.affiliation: University of Neuchâtel, Laboratory of Soil Biology, Rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland.
authors.forename: Enrique
authors.initials: E
authors.lastname: Lara
authors.affiliation: School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne EPFL, Ecological Systems Laboratory (ECOS), Station 2, 1015 Lausanne, Switzerland.|Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Site Lausanne, Station 2, 1015 Lausanne, Switzerland.
authors.forename: Robert T E
authors.initials: RT
authors.lastname: Mills
authors.affiliation: University of Neuchâtel, Laboratory of Soil Biology, Rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland.|Jardin Botanique de Neuchâtel, Pertuis-du-Sault 56-58, CH-2000 Neuchâtel, Switzerland.
authors.forename: Edward A D
authors.initials: EA
authors.lastname: Mitchell
authors.affiliation: Environment, University of York, Heslington, York, YO10 5DD, UK.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Payne
authors.affiliation: School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne EPFL, Ecological Systems Laboratory (ECOS), Station 2, 1015 Lausanne, Switzerland.|Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Site Lausanne, Station 2, 1015 Lausanne, Switzerland.
authors.forename: Bjorn J M
authors.initials: BJ
authors.lastname: Robroek
mesh_terms: D001419:Bacteria / Q000378:metabolism; D018533:Biomass; D002244:Carbon / Q000378:metabolism*; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism; D057231:Climate Change; D017753:Ecosystem; D004734:Energy Metabolism; D005658:Fungi / Q000378:metabolism; D044003:Sphagnopsida / Q000378:metabolism
chemical_list: D002245:Carbon Dioxide; D002244:Carbon