Influence of hydrological fluxes on the structure of nitrate-reducing bacteria communities in a peatland N. Bougon a, b, c , L. Aquilina a, c , M.P. Briand b, c , S. Coedel d , P. Vandenkoornhuyse b, c, * a IFR2116/FR 90 CAREN- UMR 6118 Ge´osciences, Universite´ de Rennes 1, Campus de Beaulieu, Avenue Leclerc, F-35042 Rennes, France b IFR2116/FR 90 CAREN- UMR 6553 EcoBio, Universite ´ de Rennes 1, Campus de Beaulieu, Avenue Leclerc, F-35042 Rennes, France c Universite´ Europe´enne de Bretagne, UEB (European University of Brittany), France d Plateforme ge´notypage Ouest Ge ´nopole, INRA Rennes, 35650 Le Rheu, France article info Article history: Received 8 September 2008 Received in revised form 9 March 2009 Accepted 21 March 2009 Available online 16 April 2009 Keywords: Microbial diversity Environmental changes Hydrological flowpaths Denitrification Nitrate reducers narG T-RFLP abstract Factors influencing nitrate dynamics and nitrate-reducing bacteria in peat soil in the field, were inves- tigated in laboratory experiments. A previous study had indicated that the on-site effects of redox conditions and nutrient fluxes on microbial activity were influenced by hydrological conditions. However, the laboratory experiments indicated that peat samples from sites under different hydrological regimes exhibited different microbial activities independently of oxygenation conditions. The effects of redox conditions and nutrient fluxes (i.e. influence of NO 3  and O 2 concentration) on the nitrate reducer community were therefore assessed. Microbial community structures in peat samples from sites under different hydrologic regimes were compared using Terminal-Restriction Fragment Length Polymorphism diversity signatures of the narG gene. This gene encodes the catalytic subunit of the nitrate reductase. Unexpectedly, the nitrate reducer communities were very similar at the beginning of the experiment whatever the peatland soil analysed. However, a strong structuration and divergence within the nitrate reducer communities, that was site-dependent, was evident after 76 h of incubation. These modifications within the microbial communities seemed to be due to differences in peat saturation at the sampling sites resulting from the different hydrological regimes. Of the forcing variables tested, oxygenation had a slight effect on the composition of the nitrate-reducers’ community whereas nitrate addition had no effect. This study shows that a physical constraint such as hydrological regime might be considered important in microbial community composition. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Much work has been done on the denitrification process (e.g.: Schlesinger, 1997) due to their importance in nitrogen cycling and the significance of N on a global scale. NO and N 2 O emissions from ecosystems to the atmosphere during N cycling impact global warming (Prather et al., 2001). The NO and N 2 O budget in the atmosphere is mainly controlled by denitrification (Conrad, 1996), and modifications in community composition or activity might have important effects on N turnover and ecosystem functioning (e.g.: Perry et al., 1989; Øvreås, 2000). The interactions between microbial diversity and biogeochem- ical processes, especially in wetlands and river sediments, have already been addressed in order to better understand the factors affecting nitrate reduction through denitrification, (e.g.: Hedin et al., 1998; Bilanovic et al., 1999; Ostrom et al., 2002; Cannavo et al., 2004). Denitrifiers and more specifically nitrate-reducing bacteria, because they are a phylogenetically highly diversified group of soil micro-organisms, are generally considered as good models for studying the influence of microbial diversity on soil ecosystem functioning (Zumft, 1997; Gregory et al., 2000; Philippot, 2002; Deiglmayr et al., 2004). Denitrifying and nitrate-reducing bacterial communities from soils are known to be sensitive to environmental conditions such as chemical stress and environmental disturbance (Øvreås, 2000; Denaro et al., 2005; Schimel et al., 2007; Ge et al., 2008). Wallenstein et al. (2006) highlighted the importance of temperature and moisture conditions, substrate availability, competition and disturbances in controlling the denitrifiers and more specifically nitrate-reducing bacterial community. The same authors (Wallenstein et al., 2006) pointed out the importance of environmental conditions and resources such as N pool, oxygena- tion, carbon availability, and pH on instantaneous denitrification rates. However, the effects of physical parameters such as hydro- logical regime on denitrification processes and microbial * Corresponding author. IFR2116/FR 90 CAREN- UMR 6553 EcoBio, Universite ´ de Rennes 1, Campus de Beaulieu, Avenue Leclerc, F-35042 Rennes, France. Tel.: þ33 2 23 23 65 89; fax: þ33 2 23 23 60 90. E-mail address: philippe.vandenkoornhuyse@univ-rennes1.fr (P. Vandenkoornhuyse). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2009.03.015 Soil Biology & Biochemistry 41 (2009) 1289–1300