Experimental warming differentially affects microbial structure and activity in two contrasted moisture sites in a Sphagnum-dominated peatland

Frédéric Delarue (1) , Alexandre Buttler (2, 3, 4) , Luca Bragazza (5) , Laurent Grasset (6) , Vincent E. J. Jassey (2, 4) , Sébastien Gogo (1) , Fatima Laggoun-Défarge (1)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 WSL - Institut Fédéral de Recherches sur la Forêt, la Neige et le Paysage
3 LCE - Laboratoire Chrono-environnement (UMR 6249)
4 CMCS-EPFL - CMCS-EPFL
5 Biology and Evolution, University of Ferrara
6 SRSN - Synthèse et réactivité des substances naturelles

Several studies on the impact of climate warming have indicated that peat decomposition/mineralizationwill be enhanced. Most of these studies deal with the impact of experimental warming during summer when prevalent abiotic conditions are favorable to decomposition. Here, we investigated the effect of experimental air warming by open-top chambers (OTCs) onwater-extractable organic matter (WEOM), microbial biomasses and enzymatic activities in two contrasted moisture sites named Bog and Fen sites, the latter considered as the wetter ones. While no or few changes in peat temperature and water content appeared under the overall effect of OTCs, we observed that air warming smoothed water content differences and led to a decrease in mean peat temperature at thewarmed Bog sites. This thermal discrepancy between the two sites led to contrasting changes in microbial structure and activities: a rise in hydrolytic activity at the warmed Bog sites and a relative enhancement of bacterial biomass at thewarmed Fen sites. These featureswere not associated with any change inWEOMproperties namely carbon and sugar contents and aromaticity, suggesting that air warming did not trigger any shift in OM decomposition. Using various tools, we show that the use of single indicators of OM decomposition can lead to fallacious conclusions. Lastly, these patterns may change seasonally as a consequence of complex interactions between groundwater level and air warming, suggesting the need to improve our knowledge using a high time-resolution approach.

Keywords: Carbon Climate change Enzymes Microbial biomass Moisture Open-top chambers

Domains: Continental interfaces, environment

Frédéric Delarue, Alexandre Buttler, Luca Bragazza, Laurent Grasset, Vincent E. J. Jassey, et al.. Experimental warming differentially affects microbial structure and activity in two contrasted moisture sites in a Sphagnum-dominated peatland. Science of the Total Environment, 2015, 511, pp.576 - 583. ⟨10.1016/j.scitotenv.2014.12.095⟩. ⟨insu-01105287⟩