An unexpected role for mixotrophs in the response of peatland carbon cycling to climate warming

Vincent E.J. Jassey (1, 2) , Constant Signarbieux (2, 1) , Stephan Hättenschwiler (3) , Luca Bragazza (4, 2, 1) , Alexandre Buttler (5, 2, 1) , Frédéric Delarue (6) , Bertrand Fournier (7, 8) , Daniel Gilbert (5) , Fatima Laggoun-Défarge (6) , Enrique Lara (9) , Robert T.E. Mills (2, 1) , Edward A. D. Mitchell (10, 11) , Richard Payne (12) , Bjorn J.M. Robroek (2, 1)

1 Swiss Federal Institute for Forest, Snow and Landscape Research WSL
2 ENAC - School of Architecture, Civil and Environmental Engineering
3 CEFE - Centre d’Ecologie Fonctionnelle et Evolutive
4 UniFE - Università degli Studi di Ferrara = University of Ferrara
5 LCE - Laboratoire Chrono-environnement (UMR 6249)
6 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
7 Laboratoire de biodiversité du sol [Neuchâtel]
8 WSL Lausanne
9 Institute of Biology - Laboratory of Soil Biology
10 Jardin Botanique de Neuchâtel
11 Institute of Biology - Laboratory of Soil Biology
12 MMU - Manchester Metropolitan University

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. The vast majority of the Earth's organisms meet their requirements for carbon (C) and energy either by utilising light to assimilate CO 2 through photosynthesis (autotrophy), or by the uptake of organic C compounds (heterotrophy). However, some organisms have the potential to combine auto-and heterotrophic C uptake, a strategy termed 'mixotrophy'

Domaines: Planète et Univers [physics]; Interfaces continentales, environnement

Vincent E.J. Jassey, Constant Signarbieux, Stephan Hättenschwiler, Luca Bragazza, Alexandre Buttler, et al.. An unexpected role for mixotrophs in the response of peatland carbon cycling to climate warming. Scientific Reports, 2015, 5 (Article number: 16931), pp.1-10. ⟨10.1038/srep16931⟩. ⟨insu-01240013⟩