A survey of denitrifying communities in a wetland

1 p.A hydrological and geochemical survey of a wetland (Normandy, France) highlighted the presence of a major spatiotemporal variability of sulphates and nitrates concentrations related to a distinct hydrologic regime represented by the stream proximity. An experimental approach was carried out to determine the factors influencing the dynamic of nitrate and sulphate concentrations observed in field; and the denitrifiers' community structuration related to different environmental stresses. We investigated the effects of stream proximity and associated nutrients fluxes, on microbial activity. Experiments were performed with peat sampled from different plots along a hydrologic flow gradient to characterize the biogeochemical processes and estimate the potential reactivity. We used bioreactors containing the peat-soils and a synthetic solution (similar to the field stream composition) to understand biogeochemical fluxes related to different nitrate availability and redox conditions. The evolution of nitrates and sulphates concentrations was analysed over time. The results demonstrated a spatial variability of the potential reactivity and a biological activity reacting unevenly to experimental conditions. We highlighted the control of the temporal evolution of nitrate and sulphate concentration by redox conditions and nitrate availability (nitrates, P<0.001; sulphates, P<0.001) and by distinct hydrologic regime (nitrates, P <0,001; sulphates, P<0,001). We established the reduction of nitrate is a heterotrophic denitrification and the sulphate production is related to bio-geochemical processes. The fate of microbial activity seems to be regulated by hydrogeological fluxes especially at the stream-soil, soil-water interface. Spatial and temporal dynamic of denitrifying community composition is currently investigated by a narG gene analysis and t-RFLP

Influence of hydrological fluxes on the structure of nitrate-reducing bacteria communities in a peatland

International audienceFactors influencing nitrate dynamics and nitrate-reducing bacteria in peat soil in the field, were investigated 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 NO3 and O2 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

Effects of soil engineers in C-N-S coupling in a regenerating cutover peatland.

communication affiché

Role of soil engineers in the transfers of C, N, S in a regenerating cutover peatland.

communication oral

Role of soil engineers in the transfers of C, N, S in a regenerating cutover peatland.

communication oral

Short-term changes in the structure of microbial communities following bare peat recolonization by Agrostis stolonifera and Eriophorum angustifolium.

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